Method for indicating precoding vector, method for determining precoding vector, and communications apparatus

ABSTRACT

This application discloses methods and apparatuses for determining precoding vector. One example method includes: determining, by a network apparatus, a precoding vector of one or more frequency domain units based on the first indication information. The first indication information is used to indicate L 1  beam vectors in a beam vector set, K 1  frequency domain vectors in a frequency domain vector set, and T 1  space-frequency component matrices. A weighted sum of the T 1  space-frequency component matrices is used to determine a precoding vector of each frequency domain unit. The T 1  space-frequency component matrices are selected from M 1  space-frequency component matrices corresponding to the L 1  beam vectors and the K 1  frequency domain vectors, each space-frequency component matrix is uniquely determined by one beam vector and one frequency domain vector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/230,523, filed on Apr. 14, 2021, which is a continuation ofInternational Application No. PCT/CN2019/110342, filed on Oct. 10, 2019.The International Application claims priority to Chinese PatentApplication No. 201811205381.1, filed on Oct. 16, 2018 and ChinesePatent Application No. 201811281059.7, filed on Oct. 30, 2018. All ofthe aforementioned patent applications are hereby incorporated byreference in their entireties.

TECHNICAL FIELD

This application relates to the wireless communications field, and morespecifically, to a method for indicating a precoding vector, a methodfor determining a precoding vector, and a communications apparatus.

BACKGROUND

In a massive multiple-input multiple-output (massive multiple-inputmultiple-output, Massive MIMO) technology, a network device may reduceinterference between a plurality of users and interference between aplurality of signal streams of a same user by precoding. This helpsimprove signal quality, implement spatial multiplexing, and improvespectrum utilization.

A terminal device may determine a precoding vector in ways such aschannel measurement to get feedback, so that the network device obtainsa precoding vector that is the same as or similar to the precodingvector determined by the terminal device. In an implementation, theterminal device may indicate the precoding vector to the network deviceby using two levels of feedback: wideband feedback and sub-bandfeedback. Specifically, the terminal device may indicate, based on eachtransport layer, selected beam vectors and a quantized value of awideband amplitude coefficient of each beam vector by using the widebandfeedback, and may indicate, by using the sub-band feedback, a quantizedvalue of a combination coefficient that can be used for each sub-band,where the combination coefficient may include, for example, a sub-bandamplitude coefficient and a sub-band phase coefficient. The networkdevice may restore precoding vectors corresponding to the sub-bands byusing both information in the wideband feedback and information in thesub-band feedback. For a specific method used by the terminal device toindicate the precoding vector to the network device by using the twolevels of feedback: the wideband feedback and the sub-band feedback,refer to a type II (type II) codebook feedback manner defined in the newradio (new radio, NR) protocol TS 38.214.

However, as a quantity of transport layers increases, feedback overheadsbrought by the foregoing feedback mode multiply. A larger quantity ofsubbands leads to a greater increase in the feedback overheads.

SUMMARY

This application provides a method for indicating a precoding vector, amethod for determining a precoding vector, and a communicationsapparatus, to reduce feedback overheads.

According to a first aspect, a method for indicating a precoding vectoris provided. The method may be performed by a terminal device, or may beperformed by a chip disposed in a terminal device.

Specifically, the method includes: generating first indicationinformation; and sending the first indication information. The firstindication information is used to indicate L₁ beam vectors in a beamvector set, K₁ frequency domain vectors in a frequency domain vectorset, and T₁ space-frequency component matrices, and a weighted sum ofthe T₁ space-frequency component matrices is used to determine aprecoding vector of one or more frequency domain units, where the L₁beam vectors and the K₁ frequency domain vectors correspond to M₁space-frequency component matrices, the T₁ space-frequency componentmatrices are a part of the M₁ space-frequency component matrices, eachof the M₁ space-frequency component matrices is uniquely determined byone of the L₁ beam vectors and one of the K₁ frequency domain vectors,and M₁=L₁×K₁; the L₁ beam vectors are a part of beam vectors in the beamvector set, and/or the K₁ frequency domain vectors are a part offrequency domain vectors in the frequency domain vector set; and M₁, L₁,K₁, and T₁ are all positive integers.

According to a second aspect, a method for determining a precodingvector is provided. The method may be performed by a network device, ormay be performed by a chip disposed in a network device.

Specifically, the method includes: receiving first indicationinformation, where the first indication information is used to indicateL₁ beam vectors in a beam vector set, K₁ frequency domain vectors in afrequency domain vector set, and T₁ space-frequency component matrices,and a weighted sum of the T₁ space-frequency component matrices is usedto determine a precoding vector of one or more frequency domain units,where the L₁ beam vectors and the K₁ frequency domain vectors correspondto M₁ space-frequency component matrices, the T₁ space-frequencycomponent matrices are a part of the M₁ space-frequency componentmatrices, each of the M₁ space-frequency component matrices is uniquelydetermined by one of the L₁ beam vectors and one of the K₁ frequencydomain vectors, and M₁=L₁×K₁; the L₁ beam vectors are a part of beamvectors in the beam vector set, and/or the K₁ frequency domain vectorsare a part of frequency domain vectors in the frequency domain vectorset; and M₁, L₁, K₁, and T₁ are all positive integers; and determining aprecoding vector of one or more frequency domain units based on thefirst indication information.

In an implementation, the T₁ space-frequency component matrices areselected from the M₁ space-frequency component matrices, and the M₁space-frequency component matrices are determined based on the L₁ beamvectors and the K₁ frequency domain vectors. In another implementation,the T₁ space-frequency component matrices are determined by T₁space-frequency vector pairs in M₁ space-frequency vector pairs, the M₁space-frequency vector pairs are obtained by combining the L₁ beamvectors and the K₁ frequency domain vectors, and each space-frequencyvector pair is uniquely determined by one of the L₁ beam vectors and oneof the K₁ frequency domain vectors. In still another implementation, theT₁ space-frequency component matrices may be represented as T₁space-frequency vector pairs obtained by combining T₁ beam vectors andT₁ frequency domain vectors, and the T₁ space-frequency vector pairs areselected from M₁ space-frequency vector pairs obtained by combining theL₁ beam vectors and the K₁ frequency domain vectors.

Based on the foregoing technical solutions, the terminal deviceindicates a small quantity of beam vectors, frequency domain vectors,and space-frequency component matrices to the network device to help thenetwork device restore a precoding vector. The frequency domain vectormay be used to describe different change rules of a channel in frequencydomain. The terminal device may simulate a change of a channel infrequency domain through linear superposition of one or more frequencydomain vectors, so that a relationship between frequency domain units isfully explored, continuity of frequency domain is utilized, and a changerule on a plurality of frequency domain units is described by using arelatively small quantity of frequency domain vectors. Compared with thecurrent technology, this application does not require that a weightingcoefficient be independently reported based on each frequency domainunit, and an increase in frequency domain units does not causemultiplication of feedback overheads. Therefore, feedback overheads canbe greatly reduced while feedback precision is ensured.

However, because the beam vector set may include a relatively largequantity of beam vectors, and the frequency domain vector set mayinclude a relatively large quantity of frequency domain vectors, if arelatively small quantity of beam vectors and a relatively smallquantity of frequency domain vectors are directly indicated in the beamvector set and the frequency domain vector set, relatively high bitoverheads may be caused, or the terminal device and the network deviceneed to predefine a large quantity of correspondences between beamvector combinations and indexes and a large quantity of correspondencesbetween frequency domain vector combinations and indexes.

However, in the embodiments of this application, the terminal devicenarrows a selection range of the space-frequency component matrices thatare used for weighted summation to a range of the M₁ space-frequencycomponent matrices constructed by using the L₁ beam vectors and the K₁frequency domain vectors. That is, the terminal device first selects arelatively small range of vectors from an existing vector set, and thenselects T₁ space-frequency component matrices from the range andindicates the T₁ space-frequency component matrices. On one hand,relatively high feedback overheads caused by directly indicating the T₁space-frequency component matrices can be avoided. On the other hand,the terminal device and the network device may not need to store a largequantity of correspondences.

It needs to be noted that the T₁ beam vectors are a part of beam vectorsselected from the L₁ beam vectors, but it does not mean that T₁ isnecessarily smaller than L₁, and some or all of the T₁ beam vectors maybe reused. Therefore, a quantity of beam vectors used for combination toobtain T₁ beam vector pairs is T₁. Likewise, the T₁ frequency domainvectors are a part of frequency domain vectors selected from the K₁frequency domain vectors, but it does not mean that T₁ is necessarilysmaller than K₁, and some or all of the T₁ frequency domain vectors maybe reused. Therefore, a quantity of frequency domain vectors used forcombination to obtain T₁ frequency domain vector pairs is T₁. Forbrevity, descriptions of a same or similar case are omitted below.

With reference to the first aspect, in some implementations of the firstaspect, the method further includes: receiving second indicationinformation, where the second indication information is used to indicatea value or values of one or more of M₁, L₁, and K₁.

Correspondingly, with reference to the second aspect, in someimplementations of the second aspect, the method further includes:sending second indication information, where the second indicationinformation is used to indicate a value or values of one or more of M₁,L₁, and K₁.

That is, the value or the values of the one or more of M₁, L₁, and K₁may be indicated by the network device.

With reference to the first aspect, in some implementations of the firstaspect, the method further includes: sending second indicationinformation, where the second indication information is used to indicatea value or values of one or more of M₁, L₁, and K₁.

Correspondingly, with reference to the second aspect, in someimplementations of the second aspect, the method further includes:receiving second indication information, where the second indicationinformation is used to indicate a value or values of one or more of M₁,L₁, and K₁.

That is, the value or the values of the one or more of M₁, L₁, and K₁may be determined by the terminal device and reported to the networkdevice.

It should be understood that the value or the values of the one or moreof M₁, L₁, and K₁ may be alternatively predefined, for example, definedin a protocol. This is not limited in this application.

With reference to the first aspect, in some implementations of the firstaspect, the method further includes: receiving third indicationinformation, where the third indication information is used to indicatea value of T₁.

In other words, the value of T₁ may be indicated by the network device.

With reference to the first aspect, in some implementations of the firstaspect, the method further includes: sending third indicationinformation, where the third indication information is used to indicatea value of T₁.

In other words, the value of T₁ may be determined by the terminal deviceand reported by the terminal device to the network device.

It should be understood that the value of T₁ may be alternativelypredefined, for example, defined in a protocol. This is not limited inthis application.

With reference to the first aspect or the second aspect, in someimplementations, the first indication information includes locationinformation of the L₁ beam vectors in the beam vector set and locationinformation of the K₁ frequency domain vectors in the frequency domainvector set.

In other words, because the L₁ beam vectors and the K₁ frequency domainvectors correspond to the M₁ space-frequency component matrices, the M₁space-frequency component matrices may be determined by indicating theL₁ beam vectors and the K₁ frequency domain vectors. In other words, theM₁ space-frequency component matrices may be indicated by using atwo-dimensional index.

With reference to the first aspect or the second aspect, in someimplementations, the M₁ space-frequency component matrices are selectedfrom a space-frequency component matrix set or a subset of aspace-frequency component matrix set, the space-frequency componentmatrices are determined by beam vectors in the beam vector set andfrequency domain vectors in the frequency domain vector set, and eachspace-frequency component matrix in the space-frequency component matrixset is uniquely determined by one beam vector in the beam vector set andone frequency domain vector in the frequency domain vector set; and thefirst indication information includes location information of the M₁space-frequency component matrices in the space-frequency componentmatrix set or location information of the M₁ space-frequency componentmatrices in the subset of the space-frequency component matrix set.

In other words, the M₁ space-frequency component matrices may beindicated by using a one-dimensional index.

It needs to be noted that a concept of the M₁ space-frequency componentmatrices is introduced in this specification only for ease ofunderstanding. This does not mean that the terminal device definitelygenerates the M₁ space-frequency component matrices. Alternatively, theterminal device may obtain the M₁ space-frequency vector pairs bycombining the L₁ beam vectors and the K₁ frequency domain vectors.However, it may be understood that the M₁ space-frequency componentmatrices may be constructed by using the L₁ beam vectors and the K₁frequency domain vectors, or by using the M₁ space-frequency vectorpairs. In other words, the M₁ space-frequency vector pairs and the M₁space-frequency component matrices may be mutually converted. Therefore,it may be considered that the M₁ space-frequency component matricescorrespond to the L₁ beam vectors and the K₁ frequency domain vectors.

Optionally, each of the M₁ space-frequency component matrices isdetermined by a product of one of the L₁ beam vectors and a conjugatetranspose of one of the K₁ frequency domain vectors.

Optionally, each of the M₁ space-frequency component matrices isdetermined by a Kronecker product of one of the K₁ frequency domainvectors and one of the L₁ beam vectors.

In the embodiments, for ease of understanding, an example in which boththe beam vector and the frequency domain vector are column vectors isused to describe a relationship between the M₁ space-frequency componentmatrices and the L₁ beam vectors and between the M₁ space-frequencycomponent matrices and the K₁ frequency domain vectors. However, thisshould not constitute any limitation on this application. For example,the frequency domain vector may alternatively be a row vector. In thiscase, each space-frequency component matrix may be determined by aproduct of one beam vector and one frequency domain vector. For anotherexample, each space-frequency component matrix may be determined by aKronecker product of one beam vector and one frequency domain vector.This is not limited in this application.

With reference to the first aspect or the second aspect, in someimplementations, the first indication information may be used toindicate the T₁ space-frequency component matrices (or the T₁space-frequency vector pairs) in any one of the following manners:

Manner 1: The T₁ space-frequency component matrices in the M₁space-frequency component matrices are indicated by using a bitmap(bitmap).

Manner 2: An index of a combination of the T₁ space-frequency componentmatrices in the M₁ space-frequency component matrices is indicated.

Manner 3: A location, in the L₁ beam vectors, of a beam vectorcorresponding to each of the T₁ space-frequency component matrices and alocation, in the K₁ frequency domain vectors, of a frequency domainvector corresponding to each of the T₁ space-frequency componentmatrices are indicated.

Manner 4: An index, in the M₁ space-frequency component matrices, ofeach of the T₁ space-frequency component matrices is indicated.

The selection range of the T₁ space-frequency component matrices can benarrowed by indicating the T₁ space-frequency component matrices in theM₁ space-frequency component matrices, so that the feedback overheads ofthe T₁ space-frequency component matrices can be reduced.

With reference to the first aspect or the second aspect, in someimplementations, the weighted sum of the T₁ space-frequency componentmatrices is used to determine a precoding vector of one or morefrequency domain units at a first transport layer.

The first transport layer may be one transport layer, or may be aplurality of transport layers.

With reference to the first aspect, in some possible implementations,the method further includes: generating fourth indication information,where the fourth indication information is used to indicate L₂ beamvectors in the beam vector set, K₂ frequency domain vectors in thefrequency domain vector set, and T₂ space-frequency component matrices,and a weighted sum of the T₂ space-frequency component matrices is usedto determine a precoding vector of one or more frequency domain units ata second transport layer, where the L₂ beam vectors and the K₂ frequencydomain vectors correspond to M₂ space-frequency component matrices, theT₂ space-frequency component matrices are a part of the M₂space-frequency component matrices, each of the M₂ space-frequencycomponent matrices is uniquely determined by one of the L₂ beam vectorsand one of the K₂ frequency domain vectors, and M₂=L₂×K₂; the L₂ beamvectors are a part of beam vectors in the beam vector set, and/or the K₂frequency domain vectors are a part of frequency domain vectors in thefrequency domain vector set; and M₂, L₂, K₂, and T₂ are all positiveintegers; and sending the fourth indication information.

With reference to the second aspect, in some possible implementations,the method further includes: receiving fourth indication information,where the fourth indication information is used to indicate L₂ beamvectors in the beam vector set and T₂ space-frequency componentmatrices, and a weighted sum of the T₂ space-frequency componentmatrices is used to determine a precoding vector of one or morefrequency domain units at a second transport layer, where the L₂ beamvectors and the K₂ frequency domain vectors correspond to M₂space-frequency component matrices, the T₂ space-frequency componentmatrices are a part of the M₂ space-frequency component matrices, eachof the M₂ space-frequency component matrices is uniquely determined byone of the L₂ beam vectors and one of the K₂ frequency domain vectors,and M₂=L₂×K₂; the L₂ beam vectors are a part of beam vectors in the beamvector set, and/or the K₂ frequency domain vectors are a part offrequency domain vectors in the frequency domain vector set; and M₂, L₂,K₂, and T₂ are all positive integers; and determining the precodingvector of the one or more frequency domain units at the second transportlayer based on the fourth indication information.

The second transport layer may be one or more transport layers otherthan the first transport layer in a plurality of transport layers.

Based on the fourth indication information, the terminal device mayindicate, to the network device, the determined precoding vector of theone or more frequency domain units at the second transport layer.

With reference to the first aspect or the second aspect, in someimplementations, L₁=L₂, K₁=K₂, and T₁=T₂.

With reference to the first aspect or the second aspect, in someimplementations, L₁>L₂, K₁>K₂, or T₁>T₂.

According to a third aspect, a communications apparatus is provided, andincludes modules or units configured to perform the method according toany possible implementation of the first aspect.

According to a fourth aspect, a communications apparatus is provided,and includes a processor. The processor is coupled to a memory, and maybe configured to read and execute an instruction in the memory, toimplement the method according to any possible implementation of thefirst aspect. Optionally, the communications apparatus further includesthe memory. Optionally, the communications apparatus further includes acommunications interface, and the processor is coupled to thecommunications interface.

In an implementation, the communications apparatus is a terminal device.When the communications apparatus is the terminal device, thecommunications interface may be a transceiver or an input/outputinterface.

In another implementation, the communications apparatus is a chipdisposed in a terminal device. When the communications apparatus is thechip disposed in the terminal device, the communications interface maybe an input/output interface.

Optionally, the transceiver may be a transceiver circuit. Optionally,the input/output interface may be an input/output circuit.

According to a fifth aspect, a communications apparatus is provided, andincludes modules or units configured to perform the method according toany possible implementation of the second aspect.

According to a sixth aspect, a communications apparatus is provided, andincludes a processor. The processor is coupled to a memory, and may beconfigured to read and execute an instruction in the memory, toimplement the method according to any possible implementation of thesecond aspect. Optionally, the communications apparatus further includesthe memory. Optionally, the communications apparatus further includes acommunications interface, and the processor is coupled to thecommunications interface.

In an implementation, the communications apparatus is a network device.When the communications apparatus is the network device, thecommunications interface may be a transceiver or an input/outputinterface.

In another implementation, the communications apparatus is a chipdisposed in a network device. When the communications apparatus is thechip disposed in the network device, the communications interface may bean input/output interface.

Optionally, the transceiver may be a transceiver circuit. Optionally,the input/output interface may be an input/output circuit.

According to a seventh aspect, a processor is provided, and includes aninput circuit, an output circuit, and a processing circuit. Theprocessing circuit is configured to: receive an input signal via theinput circuit, and output a signal via the output circuit, so that theprocessor performs the method according to any one of the first aspect,the possible implementations of the first aspect, the second aspect, orthe possible implementations of the second aspect.

In a specific implementation process, the processor may be a chip, theinput circuit may be an input pin, the output circuit may be an outputpin, and the processing circuit may be a transistor, a gate circuit, atrigger, various logic circuits, or the like. The input signal receivedby the input circuit may be received and input by, for example, but notlimited to, a receiver, the signal output by the output circuit may beoutput to, for example, but not limited to, a transmitter andtransmitted by the transmitter, and the input circuit and the outputcircuit may be a same circuit, where the circuit is used as the inputcircuit and the output circuit at different moments. Specificimplementations of the processor and the various circuits are notlimited in the embodiments of this application.

According to an eighth aspect, a processing apparatus is provided, andincludes a processor and a memory. The processor is configured to: readan instruction stored in the memory, receive a signal via a receiver,and transmit a signal via a transmitter, to perform the method accordingto any one of the first aspect, the possible implementations of thefirst aspect, the second aspect, or the possible implementations of thesecond aspect.

Optionally, there are one or more processors and one or more memories.

Optionally, the memory may be integrated into the processor, or thememory and the processor may be separately disposed.

In a specific implementation process, the memory may be a non-transitory(non-transitory) memory, for example, a read-only memory (read onlymemory, ROM). The memory and the processor may be integrated on a samechip, or may be separately disposed on different chips. A type of thememory and a manner of disposing the memory and the processor are notlimited in the embodiments of this application.

It should be understood that a related data communication process, forexample, sending indication information, may be a process of outputtingthe indication information from the processor, and receiving capabilityinformation, may be a process of receiving the input capabilityinformation by the processor. Specifically, data output by the processormay be output to the transmitter, and input data received by theprocessor may be from the receiver. The transmitter and the receiver maybe collectively referred to as a transceiver.

The processing apparatus according to the eighth aspect may be one ormore chips. The processor may be implemented by using hardware, or maybe implemented by using software. When the processor is implemented byusing the hardware, the processor may be a logic circuit, an integratedcircuit, or the like. When the processor is implemented by using thesoftware, the processor may be a general-purpose processor, and isimplemented by reading software code stored in the memory. The memorymay be integrated into the processor, or may be located outside theprocessor and exist independently.

According to a ninth aspect, a computer program product is provided. Thecomputer program product includes a computer program (also referred toas code or an instruction). When the computer program is run, a computeris enabled to perform the method according to any one of the firstaspect, the possible implementations of the first aspect, the secondaspect, or the possible implementations of the second aspect.

According to a tenth aspect, a computer-readable medium is provided. Thecomputer-readable medium stores a computer program (also referred to ascode or an instruction). When the computer program is run on a computer,the computer is enabled to perform the method according to any one ofthe first aspect, the possible implementations of the first aspect, thesecond aspect, or the possible implementations of the second aspect.

According to an eleventh aspect, a communications system is provided,and includes the foregoing network device and terminal device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a communications system to which amethod for indicating a precoding vector and a method for determining aprecoding vector provided in an embodiment of this application isapplicable;

FIG. 2 is a schematic flowchart of a method for indicating anddetermining a precoding vector according to an embodiment of thisapplication;

FIG. 3 is a schematic flowchart of a method for feeding back a precodingmatrix indicator (precoding matrix indicator, PMI) according to anotherembodiment of this application;

FIG. 4 is a schematic block diagram of a communications apparatusaccording to an embodiment of this application;

FIG. 5 is a schematic structural diagram of a terminal device accordingto an embodiment of this application; and

FIG. 6 is a schematic structural diagram of a network device accordingto an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

The following describes technical solutions of this application withreference to the accompanying drawings.

The technical solutions of the embodiments of this application may beapplied to various communications systems, such as a global system formobile communications (global system for mobile communications, GSM), acode division multiple access (code division multiple access, CDMA)system, a wideband code division multiple access (wideband code divisionmultiple access, WCDMA) system, a general packet radio service (generalpacket radio service, GPRS) system, a long term evolution (long termevolution, LTE) system, an LTE frequency division duplex (frequencydivision duplex, FDD) system, an LTE time division duplex (time divisionduplex, TDD), a universal mobile telecommunications system (universalmobile telecommunication system, UMTS), a worldwide interoperability formicrowave access (worldwide interoperability for microwave access,WiMAX) communications system, a 5th generation (5th generation, 5G)system, or a new radio (new radio, NR) system.

First, for ease of understanding of the embodiments of this application,a communications system shown in FIG. 1 is used as an example todescribe in detail a communications system to which the embodiments ofthis application are applicable. FIG. 1 is a schematic diagram of acommunications system 100 to which a method for indicating a precodingvector in an embodiment of this application is applicable. As shown inFIG. 1 , the communications system 100 may include at least one networkdevice, for example, a network device 110 shown in FIG. 1 . Thecommunications system 100 may further include at least one terminaldevice, for example, a terminal device 120 shown in FIG. 1 . The networkdevice 110 and the terminal device 120 may communicate with each otherthrough a wireless link. A plurality of antennas may be configured foreach communications device such as the network device 110 or theterminal device 120. For each communications device in thecommunications system 100, the configured plurality of antennas mayinclude at least one transmit antenna configured to send a signal and atleast one receive antenna configured to receive a signal. Therefore,communications devices in the communications system 100, for example,the network device 110 and the terminal device 120, may communicate witheach other by using a multi-antenna technology.

It should be understood that the network device in the communicationssystem may be any device that has a wireless transceiver function. Thenetwork device includes but is not limited to an evolved NodeB (evolvedNodeB, eNB), a radio network controller (radio network controller, RNC),a NodeB (NodeB, NB), a base station controller (base station controller,BSC), a base transceiver station (base transceiver station, BTS), a homeNodeB (for example, a home evolved NodeB, or a home NodeB, HNB), abaseband unit (baseband unit, BBU), an access point (access point, AP)in a wireless fidelity (wireless fidelity, Wi-Fi) system, a wirelessrelay node, a wireless backhaul node, a transmission point (transmissionpoint, TP), a transmission and reception point (transmission andreception point, TRP), or the like. Alternatively, the network devicemay be a gNB or a transmission point (TRP or TP) in a 5G system such asan NR system, may be one antenna panel or a group (including a pluralityof antenna panels) of antenna panels of a base station in a 5G system,or may be a network node, such as a baseband unit (BBU) or a distributedunit (distributed unit, DU), that constitute a gNB or a transmissionpoint.

In some deployments, the gNB may include a centralized unit (centralizedunit, CU) and a DU. The gNB may further include a radio frequency unit(radio unit, RU). The CU implements some functions of the gNB, and theDU implements some functions of the gNB. For example, the CU implementsfunctions of a radio resource control (radio resource control, RRC)layer and a packet data convergence protocol (packet data convergenceprotocol, PDCP) layer, and the DU implements functions of a radio linkcontrol (radio link control, RLC) layer, a media access control (mediaaccess control, MAC) layer, and a physical (physical, PHY) layer.Information at the RRC layer is eventually converted into information atthe PHY layer, or is converted from information at the PHY layer.Therefore, in this architecture, higher layer signaling such as RRClayer signaling may also be considered as being sent by the DU or sentby the DU and the RU. It may be understood that the network device maybe a CU node, a DU node, or a device including a CU node and a DU node.In addition, the CU may be a network device in an access network (radioaccess network, RAN), or may be a network device in a core network (corenetwork, CN). This is not limited in this application.

It should be further understood that the terminal device in the wirelesscommunications system may also be referred to as user equipment (userequipment, UE), an access terminal, a subscriber unit, a subscriberstation, a mobile station, a mobile console, a remote station, a remoteterminal, a mobile device, a user terminal, a terminal, a wirelesscommunications device, a user agent, or a user apparatus. The terminaldevice in the embodiments of this application may be a mobile phone(mobile phone), a tablet computer (pad), a computer with a wirelesstransceiver function, a virtual reality (virtual reality, VR) terminaldevice, an augmented reality (augmented reality, AR) terminal device, awireless terminal in industrial control (industrial control), a wirelessterminal in self driving (self driving), a wireless terminal intelemedicine (remote medical), a wireless terminal in a smart grid(smart grid), a wireless terminal in transportation safety(transportation safety), a wireless terminal in a smart city (smartcity), a wireless terminal in a smart home (smart home), or the like. Anapplication scenario is not limited in the embodiments of thisapplication.

It should be further understood that FIG. 1 is only a simplifiedschematic diagram of an example for ease of understanding. Thecommunications system 100 may further include another network device oranother terminal device, which is not shown in FIG. 1 .

For ease of understanding of the embodiments of this application, thefollowing briefly describes a processing process of a downlink signal ata physical layer before the downlink signal is sent. It should beunderstood that the processing process of the downlink signal describedbelow may be performed by the network device, or may be performed by achip disposed in the network device. For ease of description, thenetwork device and the chip disposed in the network device arecollectively referred to as a network device below.

The network device may process a codeword (code word) on a physicalchannel. The codeword may be a coded bit obtained through coding (forexample, including channel coding). A codeword is scrambled (scrambling)to generate a scrambling bit. Modulation mapping (modulation mapping) isperformed on the scrambling bit, to obtain a modulation symbol. Themodulation symbol is mapped to a plurality of layers (layer), throughlayer mapping (layer mapping). The layer is also referred to as atransport layer. A modulation symbol obtained through the layer mappingis precoded (precoding), to obtain a precoded signal. The precodedsignal is mapped to a plurality of resource elements (resource element,RE) through RE mapping. These REs are then transmitted through anantenna port (antenna port) after orthogonal frequency divisionmultiplexing (orthogonal frequency division multiplexing, OFDM)modulation is performed on the REs.

It should be understood that the processing process of the downlinksignal described above is merely an example for description, and shouldnot constitute any limitation on this application. For a specificprocessing process of the downlink signal, refer to the currenttechnology. For brevity, a detailed description of the specific processis omitted herein.

To facilitate understanding of the embodiments of this application, thefollowing first briefly describes terms used in the embodiments of thisapplication.

1. Precoding technology: When a channel state is known, a network devicemay process a to-be-sent signal by using a precoding matrix that matchesa channel, so that a precoded to-be-sent signal adapts to the channel,to reduce complexity of eliminating inter-channel impact by a receivedevice. Therefore, after the to-be-sent signal is precoded, quality (forexample, a signal to interference plus noise ratio (signal tointerference plus noise ratio, SINR)) of a received signal is improved.Therefore, transmission between a transmit device and a plurality ofreceive devices can be implemented on a same time-frequency resource byusing the precoding technology. That is, multi-user multiple-inputmultiple-output (multiple user multiple input multiple output, MU-MIMO)is implemented. It should be noted that related descriptions of theprecoding technology are merely examples for ease of understanding, andare not intended to limit the protection scope of the embodiments ofthis application. In a specific implementation process, the transmitdevice may further perform precoding in another manner. For example,when channel information (for example, but not limited to a channelmatrix) cannot be learned, precoding is performed by using a presetprecoding matrix or through weighted processing. For brevity, specificcontent of the precoding manner is not further described in thisspecification.

2. Precoding matrix indicator (precoding matrix indicator, PMI): Aprecoding matrix indicator may be used to indicate a precoding matrix.The precoding matrix may be, for example, a precoding matrix determinedby a terminal device based on a channel matrix for each subband. Thechannel matrix may be determined by the terminal device through channelestimation or the like or based on channel reciprocity. However, itshould be understood that a specific method for determining theprecoding matrix by the terminal device is not limited to the foregoingdescription. For a specific implementation, refer to the currenttechnology. For brevity, details are not exhaustively described herein.

For example, the precoding matrix may be obtained by performing singularvalue decomposition (singular value decomposition, SVD) on a channelmatrix or a covariance matrix of a channel matrix, or may be obtained byperforming eigenvalue decomposition (eigenvalue decomposition, EVD) on acovariance matrix of a channel matrix. This is not limited in thisapplication. It should be understood that the foregoing enumeratedmanner of determining the precoding matrix is merely an example, andshould not constitute any limitation on this application. For the mannerof determining the precoding matrix, refer to the current technology.For brevity, detailed descriptions of a specific process of determiningthe precoding matrix are omitted herein.

The terminal device may quantize a precoding matrix for each subband,and may send a quantized value to the network device by using a PMI, sothat the network device determines, based on the PMI, a precoding matrixthat is the same as or similar to the precoding matrix determined by theterminal device. For example, the network device may directly determinethe precoding matrix for each subband based on the PMI, or may determinethe precoding matrix for each subband based on the PMI and then performfurther processing, for example, perform orthogonalization processing onprecoding matrices of different users, to determine a finally usedprecoding matrix. Therefore, the network device can determine aprecoding matrix that adapts to a channel for each subband, to performprecoding processing on a to-be-sent signal. It should be understoodthat for a specific method for determining, by the network device basedon the PMI, the precoding matrix used for each subband, refer to thecurrent technology. This is merely an example for ease of understanding,and should not constitute any limitation on this application.

In conclusion, the precoding matrix determined by the terminal devicemay be understood as a to-be-fed-back precoding matrix. The terminaldevice may indicate the to-be-fed-back precoding matrix by using thePMI, so that the network device restores the precoding matrix based onthe PMI. It may be understood that the precoding matrix restored by thenetwork device based on the PMI may be the same as or similar to theto-be-fed-back precoding matrix.

A simple example of a precoding matrix fed back by using two levels whena rank (rank) is 1 is shown below.

${W = {{W_{1}W_{2}} = \begin{bmatrix}{a_{0}v_{0}} & {a_{1}v_{1}} & {a_{2}v_{2}} & {a_{3}v_{3}} & & & & \\ & & & & {a_{4}v_{0}} & {a_{5}v_{1}} & {a_{6}v_{2}} & {a_{7}v_{3}}\end{bmatrix}}}{\begin{bmatrix}c_{0} \\c_{1} \\c_{2} \\c_{3} \\c_{4} \\c_{5} \\c_{6} \\c_{7}\end{bmatrix} = {\begin{bmatrix}{{a_{0}c_{0}v_{0}} + {a_{1}c_{1}v_{1}} + {a_{2}c_{2}v_{2}} + {a_{3}c_{3}v_{3}}} \\{{a_{4}c_{4}v_{0}} + {a_{5}c_{5}v_{1}} + {a_{6}c_{6}v_{2}} + {a_{7}c_{7}v_{3}}}\end{bmatrix} \circ}}$

W represents a precoding matrix to be fed back at one transport layer,on one subband, and in two polarization directions. W₁ may be fed backby using a wideband, and W₂ may be fed back by using a subband. v₀ to v₃are beam vectors included in W₁, and the plurality of beam vectors maybe indicated by using, for example, an index of a combination of theplurality of beam vectors. In the precoding matrix shown above, beamvectors in the two polarization directions are the same, and the beamvectors v₀ to v₃ are used in both of the two polarization directions. a₀to a₇ are wideband amplitude coefficients included in W₁, and may beindicated by using quantized values of the wideband amplitudecoefficients. c₀ to c₇ are subband coefficients included in W₂, and eachsubband coefficient may include a subband amplitude coefficient and asubband phase coefficient. For example, c₀ to c₇ may include subbandamplitude coefficients α₀ to α₇ and subband phase coefficients φ₀ to φ₇,respectively, and may be indicated by using quantized values of thesubband amplitude coefficients α₀ to α₇ and quantized values of thesubband phase coefficients φ₀ to φ₇, respectively. It can be learnedthat the to-be-fed-back precoding matrix may be considered as a weightedsum of the plurality of beam vectors.

It should be understood that the precoding matrix shown above isobtained based on feedback at one transport layer, and therefore mayalso be referred to as a precoding vector. When a quantity of transportlayers increases, the terminal device may separately perform feedbackbased on each transport layer. A precoding matrix of one subband may beconstructed based on a precoding vector obtained through the feedback ateach transport layer. For example, if there are four transport layers,the precoding matrix may include four precoding vectors that arerespectively corresponding to the four transport layers.

As the quantity of transport layers increases, feedback overheads of theterminal device also increase. For example, when there are fourtransport layers, feedback overheads for a₀ to a₇ and c₀ to c₇ are atmost four times those at one transport layer. In other words, if theterminal device performs the foregoing wideband feedback and subbandfeedback based on each transport layer, feedback overheads multiply asthe quantity of transport layers increases. A larger quantity ofsubbands leads to a greater increase in the feedback overheads.Therefore, it is expected to provide a method that can reduce PMIfeedback overheads.

It should be understood that the foregoing enumerated manner of feedingback the precoding matrix by using the PMI is merely an example, andshould not constitute any limitation on this application. For example,alternatively, the terminal device may feed back a channel matrix to thenetwork device by using the PMI, and the network device may determinethe channel matrix based on the PMI, to determine a precoding matrix.This is not limited in this application.

3. Precoding vector: In the embodiments of this application, a precodingvector may be determined by a vector, for example, a column vector, inthe precoding matrix. To be specific, the precoding matrix may includeone or more column vectors, and each column vector may be used todetermine one precoding vector. When a precoding matrix includes onlyone column vector, the precoding matrix may also be referred to as aprecoding vector.

A precoding matrix may be determined by a precoding vector or precodingvectors at one or more transport layers, and each vector in theprecoding matrix may correspond to one transport layer. It is assumedthat the precoding vector may have a dimension of N₁×1. If a quantity oftransport layers is R (R is a positive integer), the precoding matrixmay have a dimension of N₁×R. The quantity of transport layers may beindicated by using a rank indicator (rank indicator, RI), N₁ mayrepresent a quantity of antenna ports, and N₁ is a positive integer.

When a plurality of polarization directions are configured for atransmit antenna, a precoding vector may alternatively be a component ofa precoding matrix at one transport layer in one polarization direction.It is assumed that a quantity of polarization directions is P (P is apositive integer), and a quantity of antenna ports in one polarizationdirection is N₂. In this case, a dimension of a precoding vectorcorresponding to one transport layer is (P×N₂)×1, and a dimension of aprecoding vector in one polarization direction may be N₂×1, where N₂ isa positive integer.

Therefore, the precoding vector may correspond to one transport layer,may correspond to one polarization direction at one transport layer, ormay correspond to another parameter. This is not limited in thisapplication.

4. Antenna port: An antenna port may be referred to as a port for short.The antenna port may be understood as a transmit antenna identified by areceive device, or a transmit antenna that can be distinguished inspace. One antenna port may be configured for each virtual antenna, eachvirtual antenna may be a weighted combination of a plurality of physicalantennas, and each antenna port may correspond to one reference signal.Therefore, each antenna port may be referred to as a reference signalport, for example, a CSI-RS port or a sounding reference signal(sounding reference signal, SRS) port.

5. Beam and beam vector: A beam may be understood as a distribution ofsignal strength formed in a direction in space. A technology of beamforming may be a beamforming (or referred to as beamforming) technologyor another technology. The beamforming technology may be specifically adigital beamforming technology, an analog beamforming technology, or ahybrid digital/analog beamforming technology. In the embodiments of thisapplication, a beam may be formed by using a digital beamformingtechnology.

A beam vector may correspond to the beam, and may be a precoding vectorin a precoding matrix, or may be a beamforming vector. Each element inthe beam vector may represent a weight of each antenna port. Weightedsignals at different antenna ports are superimposed to form an area withrelatively strong signal strength.

In the embodiments of this application, the beam vector may also bereferred to as a spatial vector. Optionally, a length (or a dimension)of the beam vector is a quantity of antenna ports in one polarizationdirection.

It is assumed that the length of the beam vector is N_(s). The beamvector may be a column vector having a dimension of N_(s)×1, or may be arow vector having a dimension of 1×N_(s). This is not limited in thisapplication.

6. Frequency domain unit: A frequency domain unit is a unit of afrequency domain resource, and may represent different frequency domainresource granularities. The frequency domain unit may include, but isnot limited to, a subband, a resource block (resource block, RB), asubcarrier, a resource block group (resource block group, RBG), aprecoding resource block group (precoding resource block group, PRG),and the like.

7. Frequency domain vector: A frequency domain vector is a vector thatis proposed in the embodiments of this application and that is used toindicate a change rule of a channel in frequency domain. The frequencydomain vector may be specifically used to represent a change rule of aweighting coefficient of each beam vector on each frequency domain unit.This change rule may be related to a multipath delay. When a signal istransmitted on a radio channel, there may be different transmissiondelays on different propagation paths. Therefore, different frequencydomain vectors may be used to represent a change rule of delays ondifferent propagation paths.

A dimension of a frequency domain vector may be a quantity of frequencydomain units on which CSI measurement needs to be performed. Becausequantities of frequency domain units on which CSI measurement needs tobe performed may be different at different moments, a dimension of afrequency domain vector may also change. In other words, the dimensionof the frequency domain vector is variable.

Optionally, a length (or the dimension) of the frequency domain vectoris a quantity of frequency domain units included in a frequency domainoccupation bandwidth of a CSI measurement resource.

The frequency domain occupation bandwidth of the CSI measurementresource may be a bandwidth used to transmit a reference signal. Thereference signal herein may be a reference signal, for example, aCSI-RS, used for channel measurement. The frequency domain occupationbandwidth of the CSI measurement resource may be, for example, less thanor equal to a pilot transmission bandwidth (or referred to as ameasurement bandwidth). In an NR system, signaling used to indicate thefrequency domain occupation bandwidth of the CSI measurement resourcemay be, for example, a CSI-frequency occupation range (CSI-FrequencyOccupation).

It should be understood that the frequency domain occupation bandwidthof the CSI measurement resource is named only for ease of description,and should not constitute any limitation on this application. Thisapplication does not exclude a possibility of expressing a same meaningby using another name.

Optionally, the length of the frequency domain vector is a length ofsignaling used to indicate a quantity of to-be-reported frequency domainunits and locations of the to-be-reported frequency domain units.

In the NR system, the signaling used to indicate the quantity of theto-be-reported frequency domain units and the locations of theto-be-reported frequency domain units may be a reporting band (reportingband). For example, the signaling may be used to indicate the quantityof the to-be-reported frequency domain units and the locations of theto-be-reported frequency domain units by using a bitmap. Therefore, thedimension of the frequency domain vector may be a quantity of bits inthe bitmap. It should be understood that the reporting band is merely apossible name of the signaling, and should not constitute any limitationon this application. This application does not exclude a possibility ofnaming the signaling by using another name to implement a same orsimilar function.

Optionally, the length of the frequency domain vector is a quantity ofto-be-reported frequency domain units.

For example, the quantity of to-be-reported frequency domain units maybe indicated by using the foregoing signaling of reporting band. Thequantity of to-be-reported frequency domain units may be all or some offrequency domain units in the frequency domain occupation bandwidth ofthe CSI measurement resource. Alternatively, the quantity ofto-be-reported frequency domain units may be the same as a signalinglength of the reporting band, or may be less than a signaling length ofthe reporting band. This is not limited in this application.

When it is defined in a protocol that the length of the frequency domainvector is one of the foregoing enumerated items, it may be consideredthat either the signaling used to indicate the frequency domainoccupation bandwidth of the CSI measurement resource or signaling usedto indicate the quantity of the to-be-reported frequency domain unitsand the locations of the to-be-reported frequency domain units is usedto implicitly indicate the length of the frequency domain vector. Forease of differentiation and description, indication information used forthe length of the frequency domain vector is denoted as fifth indicationinformation. The fifth indication information may be the signaling usedto indicate the frequency domain occupation bandwidth of the CSImeasurement resource, may be the signaling used to indicate the quantityof the to-be-reported frequency domain units and the locations of theto-be-reported frequency domain units, or may be signaling newly addedin a future protocol. This is not limited in this application.

Assuming that the length of the frequency domain vector is N_(f), thefrequency domain vector may be a column vector having a dimension ofN_(f)×1, or may be a row vector having a dimension of 1×N_(f). This isnot limited in this application.

8. Space-frequency matrix and space-frequency component matrix: For easeof description, it is assumed in the following that a quantity ofpolarization directions of a transmit antenna is 1.

If the transmit antenna has one polarization direction, aspace-frequency matrix in the polarization direction may be constructedby using precoding vectors on different frequency domain units at onetransport layer.

In the embodiments of this application, for example, the terminal devicemay determine a to-be-fed-back precoding matrix on each frequency domainunit through channel measurement or the like. The to-be-fed-backprecoding matrix on each frequency domain unit is processed, to obtain aspace-frequency matrix corresponding to each transport layer. Forexample, for one transport layer, to-be-fed-back precoding vectors onall frequency domain units may be combined to obtain a space-frequencymatrix. The space-frequency matrix may be referred to as ato-be-fed-back space-frequency matrix. The terminal device may indicatethe to-be-fed-back space-frequency matrix by using a weighted sum of oneor more space-frequency component matrices. In other words, theto-be-fed-back space-frequency matrix may be approximately the weightedsum of the one or more space-frequency component matrices. The one ormore space-frequency component matrices may be selected from apredefined space-frequency component matrix set, or may be determinedbased on a beam vector in a predefined beam vector set and a frequencydomain vector in a predefined frequency domain vector set. This is notlimited in this application.

In a possible design, the space-frequency matrix may be a matrix havinga dimension of N_(s)×N_(f). That is, the space-frequency matrix mayinclude N_(f) column vectors whose lengths are N_(s). The N_(f) columnvectors may correspond to N_(f) frequency domain units, and each columnvector may be used to determine a precoding vector of a correspondingfrequency domain unit.

For example, the space-frequency matrix may be denoted as H, where H=[h₀h₁ . . . h_(N) _(f) ⁻¹]. h₀ To h_(N) _(f) ⁻¹ are the N_(f) columnvectors corresponding to the N_(f) frequency domain units, and eachcolumn vector may have a length of N_(s). The N_(f) column vectors maybe respectively used to determine precoding vectors of the N_(f)frequency domain units.

The space-frequency matrix may be approximately a weighted sum of one ormore space-frequency component matrices.

In the embodiments, one space-frequency component matrix may be uniquelydetermined by one beam vector and one frequency domain vector. Forexample, when both the beam vector and the frequency domain vector arecolumn vectors, one space-frequency component matrix may be a product ofone beam vector and a conjugate transpose of one frequency domainvector. When the beam vector is a column vector and the frequency domainvector is a row vector, one space-frequency component matrix may be aproduct of one beam vector and one frequency domain vector. Therefore,each space-frequency component matrix may also be a matrix having adimension of N_(s)×N_(f).

In another possible design, the space-frequency matrix may be a matrixhaving a dimension of (N_(s)×N_(f))×1, or the space-frequency matrix maybe a vector having a length of N_(s)×N_(f). In other words, thespace-frequency matrix may include only one column vector having alength of N_(s)×N_(f). In this case, the space-frequency matrix may alsobe referred to as a space-frequency vector.

For example, the space-frequency matrix may be denoted as H, where H=[h₀^(T) h₁ ^(T) . . . h_(N) _(f) ⁻¹ ^(T)]. Vectors in the matrix have beendescribed in detail above. For brevity, details are not described hereinagain.

The space-frequency vector may be approximately a weighted sum of one ormore space-frequency component vectors.

In the embodiments, one space-frequency component vector may be uniquelydetermined by one beam vector and one frequency domain vector. Forexample, when both the beam vector and the frequency domain vector arecolumn vectors, one space-frequency component vector may be a Kroneckerproduct of one beam vector and one frequency domain vector, or may be aKronecker product of one frequency domain vector and one beam vector.Therefore, each space-frequency component vector may also be a vectorhaving a length of N_(s)×N_(f). In this case, the space-frequencycomponent matrix may also be referred to as a space-frequency componentvector.

If a space-frequency component vector is determined by a Kroneckerproduct of a frequency domain vector and a beam vector, aspace-frequency vector determined by a weighted sum of a plurality ofspace-frequency component vectors may be obtained by sequentiallyconnecting N_(f) column vectors each having a length of N_(s). The N_(f)column vectors may correspond to N_(f) frequency domain units, and eachcolumn vector may be used to determine a precoding vector of acorresponding frequency domain unit.

If a space-frequency component vector is determined by a Kroneckerproduct of a beam vector and a frequency domain vector, aspace-frequency vector determined by a weighted sum of a plurality ofspace-frequency component vectors may be obtained by sequentiallyconnecting N_(s) column vectors each having a length of N_(f). N_(f)elements in each column vector may correspond to N_(f) frequency domainunits. n_(f) ^(th) elements in all of the N_(s) column vectors may besequentially connected to obtain a vector having a length of N_(s), andthe vector may be used to determine a precoding vector of an n_(f) ^(th)frequency domain unit. 0≤n_(f)≤N_(f)−1, and n_(f) is an integer.

It should be understood that the foregoing merely describes, for ease ofunderstanding, several possible forms of a space-frequency matrix in onepolarization direction, for example, a matrix having a dimension ofN_(s)×N_(f) or a vector having a length of N_(s)×N_(f). However, thisshould not constitute any limitation on this application. When aquantity of polarization directions is greater than 1, thespace-frequency matrix can still be represented in the several formsenumerated above, but a dimension of the space-frequency matrix may varywith the quantity of polarization directions. For example, when thequantity of polarization directions is 2, the space-frequency matrix maybe a matrix having a dimension of 2N_(s)×N_(f), or may be a vectorhaving a length of 2N_(s)×N_(f). 2 indicates that there are twopolarization directions.

However, the space-frequency component matrix may still be a matrixhaving a dimension of N_(s)×N_(f) or a vector having a length ofN_(s)×N_(f). Therefore, a space-frequency matrix in each polarizationdirection may be represented by a weighted sum of a plurality ofspace-frequency component matrices. In other words, a space-frequencymatrix in each polarization direction may be approximately representedas a weighted sum of a plurality of space-frequency component matrices.A plurality of space-frequency component matrices used for differentpolarization directions may be the same, or a plurality of polarizationdirections may share a plurality of same space-frequency componentmatrices. In other words, space-frequency matrices or space-frequencyvectors in a plurality of polarization directions at a same transportlayer may be constructed by using a same group of beam vectors and asame group of frequency domain vectors. However, weighting coefficientsof space-frequency component matrices in different polarizationdirections may be different.

In the embodiments of this application, a basic unit that may beobtained by performing an operation on a beam vector and a frequencydomain vector may be a space-frequency base unit, for example, aspace-frequency component matrix or a space-frequency component vector.The space-frequency base unit may correspond to one polarizationdirection. A weighted sum of base units can be spliced to form aspace-frequency matrix in a plurality of polarization directions.

It should be further understood that a specific form of thespace-frequency matrix is not limited to the foregoing examples. Forbrevity, examples are not further listed one by one herein. Withreference to the two forms in which the space-frequency component matrixis the product of the beam vector and the conjugate transpose of thefrequency domain vector and the space-frequency component matrix is theKronecker product of the frequency domain vector and the beam vector,specific processes in which the terminal device indicates a precodingvector and the network device determines a precoding vector aredescribed in detail in the following embodiments. However, this shouldnot constitute any limitation on this application. Based on a sameconcept, a person skilled in the art may perform equivalent deformationor replacement on the space-frequency component matrix. Any equivalentdeformation and replacement shall fall within the protection scope ofthis application.

As described above, in downlink channel measurement, higherapproximation between a precoding matrix determined by the networkdevice based on the PMI and a precoding matrix determined by theterminal device indicates that the precoding matrix determined by thenetwork device for data transmission is more adaptable to a channelstate. In this way, signal receive quality can be improved.

To improve spectrum resource utilization and improve a data transmissioncapability of a communications system, a network device may transmitdata to a terminal device by using a plurality of transport layers.However, when a quantity of transport layers increases, overheads causedby feedback performed by the terminal device based on each transportlayer multiply. A larger quantity of subbands leads to a greaterincrease in the feedback overheads. Therefore, it is expected to providea method that can reduce feedback overheads.

In view of this, this application provides a method for indicating anddetermining a precoding vector, to reduce PMI feedback overheads.

For ease of understanding of the embodiments of this application, thefollowing descriptions are provided.

First, in the embodiments of this application, it is assumed that aquantity of polarization directions of a transmit antenna is P (P≥1 andP is an integer), and a quantity of transport layers is R (R≥1 and R isan integer).

In the embodiments, for ease of description, when numbering is involved,numbers may be consecutive and start from 0. For example, the Rtransport layers may include a 0^(th) transport layer to an (R−1)^(th)transport layer, and the P polarization directions may include a 0^(th)polarization direction to a (P−1)^(th) polarization direction.Certainly, specific implementation is not limited thereto. For example,numbers may be consecutive and start from 1. It should be understoodthat the foregoing descriptions are all provided for ease of describingthe technical solutions provided in the embodiments of this application,but are not intended to limit the scope of this application.

Second, in the embodiments of this application, transformation of amatrix and a vector is involved in many places, and therefore, for easeof understanding, a unified description is provided herein. Asuperscript T indicates transposition. For example, A^(T) represents atranspose of a matrix (or a vector) A. A superscript * represents aconjugate transpose. For example, A* represents a conjugate transpose ofa matrix (or a vector) A. For brevity, descriptions of a same or similarcase are omitted below.

Third, in the following embodiments, an example in which both a beamvector and a frequency domain vector are column vectors is used todescribe the embodiments provided in this application. However, thisshould not constitute any limitation on this application. Based on asame concept, a person skilled in the art may further figure out morepossible representations.

Fourth, a Kronecker (Kronecker) product operation of matrices isinvolved in the embodiments of this application. In the embodiments ofthis application, the Kronecker product operation may be represented by⊗. For example, a Kronecker product of matrices A and B may be expressedas A⊗B.

A Kronecker product is a block matrix obtained by multiplying allelements in a matrix by another matrix. For example, a kp×ql-dimensionalmatrix is obtained through a Kronecker product of a k×l-dimensionalmatrix A and a p×q-dimensional matrix B. Details are as follows:

${A \otimes B} = {\begin{bmatrix}{a_{11}B} & \ldots & {a_{1l}B} \\ \vdots & \ddots & \vdots \\{a_{k1}B} & \ldots & {a_{kl}B}\end{bmatrix}.}$

For a specific definition of the Kronecker product, refer to the currenttechnology. For brevity, details are not further described in thisspecification.

Fifth, in the embodiments of this application, projection betweenvectors is involved in many places. For example, projecting a vector ato a vector b may be understood as calculating an inner product of thevector a and the vector b.

Sixth, in the embodiments of this application, “used to indicate” mayinclude “used to directly indicate” and “used to indirectly indicate”.For example, when that a piece of indication information is used toindicate information I is described, the indication information may beused to directly indicate I or indirectly indicate I. This does not meanthat the indication information definitely carries I.

The information indicated by the indication information is referred toas to-be-indicated information. In a specific implementation process,there are many manners of indicating the to-be-indicated information.For example, the to-be-indicated information, such as theto-be-indicated information itself or an index of the to-be-indicatedinformation, may be directly indicated. Alternatively, theto-be-indicated information may be indirectly indicated by indicatingother information, and there is an association relationship between theother information and the to-be-indicated information. Alternatively,only a part of the to-be-indicated information may be indicated, and theother part of the to-be-indicated information is known or agreed on inadvance. For example, specific information may also be indicated byusing a pre-agreed (for example, stipulated in a protocol) arrangementsequence of various pieces of information, to reduce indicationoverheads to some extent. In addition, a common part of all pieces ofinformation may be further identified and indicated in a unified manner,to reduce indication overheads caused by separately indicating sameinformation. For example, a person skilled in the art may understandthat a precoding matrix is formed by precoding vectors, and eachprecoding vector in the precoding matrix may have a same part in termsof composition or another attribute.

In addition, a specific indication manner may alternatively be variousexisting indication manners, for example, but not limited to, theforegoing indication manners and various combinations thereof. Fordetails of various indication manners, refer to the current technology.Details are not further described in this specification. It can belearned from the foregoing descriptions that, for example, when aplurality of pieces of information of a same type need to be indicated,manners of indicating different information may be different. In aspecific implementation process, a required indication manner may beselected according to a specific requirement. The selected indicationmanner is not limited in the embodiments of this application. In thisway, the indication manner involved in the embodiments of thisapplication should be understood as covering various methods that canenable a to-be-indicated party to learn of the to-be-indicatedinformation.

In addition, the to-be-indicated information may exist in anotherequivalent form. For example, a row vector may be represented as acolumn vector, a matrix may be represented by using a transposed matrixof the matrix or a matrix may also be represented in a form of a vectoror an array, where the vector or array may be formed by connecting rowvectors or column vectors of the matrix, and a Kronecker product of twovectors may also be represented in a form such as a product of a vectorand a transposed vector of another vector. The technical solutionsprovided in the embodiments of this application should be understood ascovering various forms. For example, some or all features involved inthe embodiments of this application should be understood as coveringvarious representations of the features.

The to-be-indicated information may be sent as a whole, or may bedivided into a plurality of pieces of sub-information for separatesending. In addition, sending periodicities and/or sending occasions ofthe sub-information may be the same or may be different. A specificsending method is not limited in this application. The sendingperiodicities and/or the sending occasions of the sub-information may bepredefined, for example, predefined according to a protocol, or may beconfigured by a transmit end device by sending configuration informationto a receive end device. The configuration information may include, forexample, but not limited to, one of or a combination of at least two ofradio resource control signaling, for example, RRC signaling, MAC layersignaling, for example, MAC-CE signaling, and physical layer signaling,for example, downlink control information (downlink control information,DCI).

Seventh, definitions of many features (for example, a Kronecker product,a PMI, a frequency domain unit, a beam, a beam vector, and a weightingcoefficient of a beam vector) in this application are merely used toexplain functions of the features by using examples. For detailedcontent of the features, refer to the current technology.

Eighth, the terms “first”, “second”, “third”, and “fourth”, and varioussequence numbers in the following embodiments are merely used fordifferentiation for ease of description, and are not used to limit thescope of the embodiments of this application. For example, the sequencenumbers are used to distinguish between different indication informationor different transport layers.

Ninth, in the following embodiments, “obtained in advance” may includebeing indicated by signaling of the network device or being predefined,for example, defined in a protocol. The foregoing “predefinition” may beimplemented by prestoring corresponding code or a corresponding table ina device (for example, including the terminal device and the networkdevice) or in another manner that can be used to indicate relatedinformation. A specific implementation of the foregoing “predefinition”is not limited in this application.

Tenth, storage involved in the embodiments of this application may bestorage in one or more memories. The one or more memories may beseparately disposed, or may be integrated into an encoder or a decoder,a processor, or a communications apparatus. Alternatively, a part of theone or more memories may be separately disposed, and a part of the oneor more memories are integrated into a decoder, a processor, or acommunications apparatus. The memory may be a storage medium in anyform. This is not limited in this application.

Eleventh, the “protocol” involved in the embodiments of this applicationmay be a standard protocol in the communications field, for example, mayinclude an LTE protocol, an NR protocol, and a related protocol appliedto a future communications system. This is not limited in thisapplication.

Twelfth, “at least one” indicates one or more, and “a plurality of”indicates two or more. The term “and/or” describes an associationrelationship between associated objects and may indicate threerelationships. For example, A and/or B may indicate the following cases:Only A exists, both A and B exist, and only B exists, where A and B maybe singular or plural. The character “/” generally indicates an “or”relationship between the associated objects. “At least one of thefollowing items (pieces)” or a similar expression means any combinationof the items, including any combination of singular items (pieces) orplural items (pieces). For example, at least one of a, b, and c mayrepresent: a, b, c, a and b, a and c, b and c, or a, b, and c. a, b, andc each may be singular or plural.

The following describes in detail, with reference to the accompanyingdrawings, the method for indicating and determining a precoding vectorprovided in the embodiments of this application.

It should be understood that the method provided in the embodiments ofthis application may be applied to a system in which communication isperformed by using a multi-antenna technology, for example, thecommunications system 100 shown in FIG. 1 . The communications systemmay include at least one network device and at least one terminaldevice. The network device and the terminal device may communicate witheach other by using a multi-antenna technology.

It should be further understood that a specific structure of anexecution body of the method provided in the embodiments of thisapplication is not particularly limited in the following embodiments,provided that a program that records code of the method provided in theembodiments of this application can be run to perform communicationaccording to the method provided in the embodiments of this application.For example, the execution body of the method provided in theembodiments of this application may be the terminal device or thenetwork device, or a functional module that is in the terminal device orthe network device and that can invoke and execute the program.

Without loss of generality, interaction between the network device andthe terminal device is used as an example below to describe in detailthe method for indicating and determining a precoding vector provided inthe embodiments of this application.

FIG. 2 is a schematic flowchart of a method 200, from a perspective ofdevice interaction, for indicating and determining a precoding vectoraccording to an embodiment of this application. As shown in the figure,the method 200 may include step 210 to step 230. The following describeseach step in the method 200 in detail.

For ease of understanding, a specific process in which a terminal deviceindicates a precoding vector based on one of one or more transportlayers and one of one or more polarization directions at the transportlayer, and a network device determines the precoding vector is firstdescribed in detail. It should be understood that a quantity oftransport layers and a quantity of polarization directions of a transmitantenna are not limited in this application. In the following example,one transport layer may be any one of one or more transport layers, andone polarization direction may be any one of one or more polarizationdirections.

In step 210, the terminal device generates first indication information,where the first indication information is used to indicate L₁ (L₁≥1 andL₁ is an integer) beam vectors in a beam vector set, K₁ (K₁≥1 and K₁ isan integer) frequency domain vectors in a frequency domain vector set,and T₁ (T₁≥1 and T₁ is an integer) space-frequency component matrices inL₁×K₁ space-frequency component matrices corresponding to the L₁ beamvectors and the K₁ frequency domain vectors. The T₁ space-frequencycomponent matrices may be determined in M₁ (M₁=L₁×K₁) space-frequencycomponent matrices corresponding to the L₁ beam vectors and the K₁frequency domain vectors. In other words, the T₁ space-frequencycomponent matrices may be a subset of the M₁ space-frequency componentmatrices. The M₁ space-frequency component matrices herein may beobtained by separately traversing the L₁ beam vectors and the K₁frequency domain vectors.

It is assumed that the selected L₁ beam vectors in the beam vector setare denoted as v_(s) ⁰, v_(s) ¹, . . . , and v_(s) ^(L) ¹ ⁻¹, and theselected K₁ frequency domain vectors in the frequency domain vector setare denoted as v_(f) ⁰, v_(f) ¹, . . . , and v_(f) ^(K) ¹ ⁻¹.

The terminal device may first traverse all beam vectors in a range from0 to L₁−1, and then traverse all frequency domain vectors in a rangefrom 0 to K₁−1, to obtain the M₁ space-frequency component matrices.

Using a product of a beam vector and a conjugate transpose of afrequency domain vector as an example, the M₁ space-frequency componentmatrices may include v_(s) ⁰(v_(f) ⁰)*, v_(s) ¹(v_(f) ⁰)*, . . . , v_(s)^(L) ¹ ⁻¹(v_(f) ⁰)*, v_(s) ⁰(v_(f) ¹)*, v_(s) ¹(v_(f) ¹)*, . . . , v_(s)^(L) ¹ ⁻¹(v_(f) ^(K) ¹ ⁻¹)*, . . . , v_(s) ⁰(v_(f) ^(K) ¹ ⁻¹)*, v_(s)¹(v_(f) ^(K) ¹ ⁻¹)*, . . . , and v_(s) ^(L) ¹ ⁻¹(v_(f) ^(K) ¹ ⁻¹)*.

Alternatively, the terminal device may first traverse all frequencydomain vectors in a range from 0 to K₁−1, and then traverse all beamvectors in a range from 0 to L₁−1, to obtain the M₁ space-frequencycomponent matrices.

Still using the product of the beam vector and the conjugate transposeof the frequency domain vector as an example, the M₁ space-frequencycomponent matrices may include v_(s) ⁰(v_(f) ⁰)*, v_(s) ⁰(v_(f) ¹)*, . .. , v_(s) ⁰(v_(f) ^(K) ¹ ⁻¹)*, v_(s) ¹(v_(f) ⁰)*, v_(s) ¹(v_(f) ¹)*, . .. , v_(s) ¹(v_(f) ^(K) ¹ ⁻¹)*, . . . , v_(s) ^(L) ¹ ⁻¹(v_(f) ⁰)*, v_(s)^(L) ¹ ⁻¹(v_(f) ¹)*, . . . , and v_(s) ^(L) ¹ ⁻¹(v_(f) ^(K) ¹ ⁻¹)*.

It should be understood that the foregoing enumerated forms of thespace-frequency component matrices are merely examples, and should notconstitute any limitation on this application. Based on the foregoingrule, the M₁ space-frequency component matrices may alternatively beobtained by using a Kronecker product of a frequency domain vector and abeam vector.

It can be learned that each of the M₁ space-frequency component matricesmay be uniquely determined by using one beam vector and one frequencydomain vector, and M₁=L₁×K₁.

When the first indication information is used to indicate the T₁space-frequency component matrices, the first indication information maybe used to indicate relative locations (for example, relative indexes orrelative numbers) of the T₁ space-frequency component matrices in the M₁space-frequency component matrices. For example, the terminal device mayindicate the T₁ space-frequency component matrices by using a bitmap, anindex of a combination of the T₁ space-frequency component matrices inthe M₁ space-frequency component matrices, an index of each of the T₁space-frequency component matrices in the M₁ space-frequency componentmatrices, or the like.

If the terminal device indicates the T₁ space-frequency componentmatrices by using a bitmap, M₁ bits may be used to indicate relativelocations of the T₁ space-frequency component matrices in the M₁space-frequency component matrices. In addition, the terminal device mayfurther indicate the L₁ beam vectors by using

log₂ C_(L) ₀ ^(L) ¹

bits, and indicate the K₁ frequency domain vectors by using

log₂ C_(K) ₀ ^(K) ¹

bits. Therefore, the terminal device may indicate the T₁ space-frequencycomponent matrices by using

log₂ C_(L) ₀ ^(L) ¹

+

log₂ C_(K) ₀ ^(K) ¹

+M₁ bits.

However, if the T₁ space-frequency component matrices are directlyindicated in the beam vector set and the frequency domain vector set,caused overheads are different. For example, the beam vector setincludes L₀ beam vectors, and the frequency domain vector set includesK₀ frequency domain vectors, where L₀≥L₁, K₀≥K₁, and L₀×K₀>L₁×K₁. The L₀beam vectors and the K₀ frequency domain vectors may correspond to L₀×K₀space-frequency component matrices.

If the terminal device directly indicates relative locations of the T₁space-frequency component matrices in the L₀×K₀ space-frequencycomponent matrices,

log₂ L₀

+

log₂ K₀

bits may be required if each space-frequency component matrix isseparately indicated. If a bitmap is used for indication, L₀×K₀ bits maybe used.

In some cases, for example, when a value of L₁ and/or a value of K₁are/is relatively small, feedback overheads can be greatly reduced.

For example, it is assumed that the beam vector set includes 16 beamvectors, the frequency domain vector set includes 10 frequency domainvectors, and 15 space-frequency component matrices are selected from 160space-frequency component matrices constructed by using the beam vectorset and the frequency domain vector set.

In the current technology, if each space-frequency component matrix isseparately indicated,

log₂16

+

log₂10

bits, that is, 8 bits, are required for each space-frequency vectormatrix, and 120 bits are required for feedback of the 15 space-frequencyvector matrices. If the 15 space-frequency component matrices areindicated by using a bitmap, 160 bits are required for feedback.

If an index of a combination of the 15 space-frequency componentmatrices is to be fed back, because vectors in the beam vector set andthe frequency domain vector set may be combined in pairs, the terminaldevice and the network device may need to prestore a large quantity ofone-to-one correspondences between combinations and indexes.

However, in this embodiment, a part of relatively strong beam vectorsand a part of relatively strong frequency domain vectors may be firstindicated in the 16 beam vectors and the 10 frequency domain vectors,and then 15 space-frequency component matrices may be selected from thepart of relatively strong beam vectors and the part of relatively strongfrequency domain vectors.

For example, assuming that eight beam vectors and five frequency domainvectors are selected, the eight beam vectors and the five frequencydomain vectors may be fed back by using

log₂ C₁₆ ⁸

bits and

log₂ C₁₀ ⁵

bits respectively, that is, 14 bits and 8 bits respectively. In 40space-frequency component matrices obtained by combining the eight beamvectors and the five frequency domain vectors, the terminal device mayfurther indicate the selected 15 space-frequency component matrices. Ifthe terminal device indicates the 15 space-frequency component matricesby using a bitmap, 40 bits may be used for indication. In this case, the15 space-frequency component matrices may be fed back by using 62 bits.Compared with the foregoing manner, this manner can greatly reduceoverheads.

It should be understood that a quantity of beam vectors, a quantity offrequency domain vectors, and a quantity of space-frequency componentmatrices that are enumerated above, and caused bit overheads are merelyexamples, and should not constitute any limitation on this application.

It should be further understood that the foregoing enumerated methodsfor indicating the T₁ space-frequency vector pairs are merely examples,and should not constitute any limitation on this application. A specificmethod for indicating the T₁ space-frequency vector pairs by theterminal device is not limited in this application.

In this embodiment, a weighted sum of the T₁ space-frequency componentmatrices may be used to determine a precoding vector of one or morefrequency domain units. Specifically, the weighted sum of the T₁space-frequency component matrices may be used to construct aspace-frequency matrix. The space-frequency matrix may include one ormore column vectors corresponding to the one or more frequency domainunits, and each column vector may be used to determine a precodingvector of a corresponding frequency domain unit. The foregoing hasdescribed in detail the relationship between the space-frequency matrixand the precoding vector. For brevity, details are not described hereinagain.

The space-frequency matrix may be approximately the weighted sum of theT₁ space-frequency component matrices. For example, the space-frequencymatrix may be denoted as H, where

$H \approx {\sum\limits_{t_{1} = 0}^{T_{1} - 1}{a_{t_{1}}{U_{t_{1}}.}}}$

represents a t₁ ^(th) space-frequency component matrix in the T₁space-frequency component matrices, and a_(t) ₁ represents a weightingcoefficient of the t₁ ^(th) space-frequency component matrix U_(t) ₁ .

The terminal device may predetermine the T₁ space-frequency componentmatrices, or may predetermine space-frequency vector pairs used togenerate the T₁ space-frequency component matrices, and then may furtherdetermine weights of the T₁ space-frequency component matrices or the T₁space-frequency vector pairs. The terminal device may indicate the T₁space-frequency component matrices and the weights of thespace-frequency component matrices to the network device, or indicatethe T₁ space-frequency vector pairs and the weights of thespace-frequency vector pairs to the network device, so that the networkdevice restores the precoding vector of the one or more frequency domainunits.

Therefore, the T₁ space-frequency component matrices indicated by thefirst indication information may be used to determine the precodingvector with reference to the weights of the space-frequency componentmatrices. The weights of the space-frequency component matrices each maybe indicated by using the first indication information, or may beindicated by using other information. This is not limited in thisapplication. For a specific method for indicating a weight of eachspace-frequency component matrix, refer to the current technology.

In this embodiment, each of the T₁ space-frequency component matricesmay be uniquely determined by one beam vector and one frequency domainvector in the T₁ space-frequency vector pairs. Therefore, the terminaldevice may directly indicate the T₁ space-frequency component matrices,may indirectly indicate the T₁ space-frequency component matrices byindicating the T₁ space-frequency vector pairs, or may directly indicatethe T₁ space-frequency vector pairs. The T₁ space-frequency vector pairsmay be considered as an equivalent form of the T₁ space-frequencycomponent matrices.

In an implementation, the T₁ space-frequency component matrices areselected from the M₁ space-frequency component matrices corresponding tothe L₁ beam vectors and the K₁ frequency domain vectors. The M₁space-frequency component matrices are determined by using the L₁ beamvectors and the K₁ frequency domain vectors, each space-frequencycomponent matrix may be uniquely determined by using one beam vector andone frequency domain vector, and M₁=L₁×K₁.

Therefore, the T₁ space-frequency component matrices may be determinedbased on the L₁ beam vectors in the beam vector set and the K₁ frequencydomain vectors in the frequency domain vector set. The terminal devicemay indicate the T₁ space-frequency component matrices based on the L₁beam vectors and the K₁ frequency domain vectors.

In another implementation, the T₁ space-frequency vector pairs may beselected from M₁ space-frequency vector pairs obtained by combining theL₁ beam vectors and the K₁ frequency domain vectors. Each of the M₁space-frequency vector pairs may be uniquely determined by using onebeam vector and one frequency domain vector, and M₁=L₁×K₁.

Therefore, the T₁ space-frequency vector pairs may be selected from theM₁ space-frequency vector pairs obtained by combining the L₁ beamvectors in the beam vector set and the K₁ frequency domain vectors inthe frequency domain vector set. The T₁ space-frequency vector pairs maybe a part of space-frequency vector pairs in the M₁ space-frequencyvector pairs. The terminal device may indicate the T₁ space-frequencyvector pairs based on the L₁ beam vectors and the K₁ frequency domainvectors, or based on the M₁ space-frequency vector pairs.

The L₁ beam vectors may be a part of beam vectors in the beam vectorset, and/or the K₁ frequency domain vectors may be a part of frequencydomain vectors in the frequency domain vector set. To be specific, whenthe L₁ beam vectors are all beam vectors in the beam vector set, the K₁frequency domain vectors are only a part of frequency domain vectors inthe frequency domain vector set; when the K₁ frequency domain vectorsare all frequency domain vectors in the frequency domain vector set, theL₁ beam vectors are only a part of beam vectors in the beam vector set;when the L₁ beam vectors are a part of beam vectors in the beam vectorset, the K₁ frequency domain vectors may be a part or all of frequencydomain vectors in the frequency domain vector set; when the K₁ frequencydomain vectors are a part of frequency domain vectors in the frequencydomain vector set, the L₁ beam vectors may be a part or all of beamvectors in the beam vector set.

It is assumed that the beam vector set includes L₀ beam vectors, and thefrequency domain vector set includes K₀ frequency domain vectors. Inthis case, L₀≥L₁, K₀≥K₁, and L₀, L₁, K₀, and K₁ do not satisfy L₀=L₁ andK₀=K₁ at the same time.

When the L₁ beam vectors are a part of beam vectors in the beam vectorset, the L₁ beam vectors may be L₁ relatively strong beam vectorsselected from the beam vector set. When the K₁ frequency domain vectorsare a part of frequency domain vectors in the frequency domain vectorset, the K₁ frequency domain vectors may be K₁ relatively strongfrequency domain vectors selected from the frequency domain vector set.The L₁ relatively strong beam vectors may be understood as L₁ beamvectors with relatively large weighting coefficients, and the K₁relatively strong frequency domain vectors may be understood as K₁ beamvectors with relatively large weighting coefficients. This is because abeam vector and a frequency domain vector with relatively largeweighting coefficients occupy a relatively large weight in a linearcombination, and also have a relatively large impact on approximateprecision of the precoding vector. The following describes in detail theL₁ relatively strong beam vectors and the K₁ relatively strong frequencydomain vectors with reference to specific implementations. Detaileddescriptions of the L₁ beam vectors and the K₁ frequency domain vectorsare temporarily omitted herein.

In conclusion, the terminal device may pre-determine the L₁ beam vectorsin the beam vector set and the K₁ frequency domain vectors in thefrequency domain vector set, narrow a selection range of the T₁space-frequency component matrices used for weighted summation to arange of the M₁ space-frequency component matrices constructed by usingthe L₁ beam vectors and the K₁ frequency domain vectors, select the T₁space-frequency component matrices from the M₁ space-frequency componentmatrices, and indicate the T₁ space-frequency component, thereby helpingreduce feedback overheads of the T₁ space-frequency component matrices.

It should be noted that a concept of the M₁ space-frequency componentmatrices is introduced herein only for ease of understanding. This doesnot mean that the terminal device definitely generates the M₁space-frequency component matrices. Alternatively, the terminal devicemay obtain the M₁ space-frequency vector pairs by combining the L₁ beamvectors and the K₁ frequency domain vectors. However, it may beunderstood that the M₁ space-frequency component matrices may beconstructed by using the L₁ beam vectors and the K₁ frequency domainvectors, or by using the M₁ space-frequency vector pairs. In otherwords, the M₁ space-frequency vector pairs and the M₁ space-frequencycomponent matrices may be mutually converted. Therefore, it may beconsidered that the M₁ space-frequency component matrices correspond tothe L₁ beam vectors and the K₁ frequency domain vectors. M₁ isintroduced only to reflect a correspondence between the M₁space-frequency component matrices (space-frequency component vectors orspace-frequency vector pairs) and the L₁ beam vectors and between the M₁space-frequency component matrices and the K₁ frequency domain vectors,and should not constitute any limitation on this application.

Values of L₁, K₁, and T₁ may be indicated by the network device, or maybe predefined, for example, may be defined in a protocol, or may bedetermined by the terminal device and then reported to the networkdevice, or may be configured by combining the foregoing enumeratedmethods.

If the values of L₁ and K₁ are indicated by the network device,optionally, the method further includes: The terminal device receivessecond indication information, where the second indication informationis used to indicate values of at least two of L₁, K₁, and M₁.Correspondingly, the network device sends the second indicationinformation.

Optionally, the second indication information is carried in higher layersignaling, for example, an RRC message.

If the values of L₁ and K₁ are determined and reported by the terminaldevice, optionally, the method further includes: The terminal devicesends second indication information, where the second indicationinformation is used to indicate a value or values of one or more of L₁,K₁, and M₁. Correspondingly, the network device receives the secondindication information.

Optionally, the second indication information is carried in uplinkcontrol information (uplink control information, UCI), for example, CSI.

Because L₁, K₁, and M₁ satisfy M₁=L₁×K₁, when values of any two of L₁,K₁, and M₁ are determined, the value of the other one can also bedetermined.

It should be understood that information used to indicate the values ofL₁, K₁, and M₁ may be same information, or may be different information.This is not limited in this application.

Optionally, the value of either L₁ or K₁ may be predefined, for example,defined in a protocol, and the value of the other one of L₁ or K₁ isindicated by the network device by using signaling.

For example, the value of L₁ may be indicated by the network device byusing signaling, and the value of K₁ may be defined in a protocol. Thevalue of K₁ is not limited in this application.

For another example, the value of L₁ may be indicated by the networkdevice by using signaling, and a calculation formula of K₁ or that thevalue of K₁ is a value of a parameter may be defined in a protocol. Forexample, the value of K₁ being a length N_(f) of a frequency domainvector, or the calculation formula of K₁, for example, K₁=

N_(f)/2

, K₁=

N_(f)/2

, or K₁=[N_(f)/2], may be defined in the protocol. In this case, it maybe understood that the value of K₁ is implicitly indicated by using thefifth indication information.

indicates rounding up,

indicates rounding down, and [ ] indicates rounding off.

For still another example, the value of K₁ may be indicated by thenetwork device by using signaling, and the value of L₁ may be defined ina protocol. The value of L₁ is not limited in this application.

For yet another example, the value of K₁ may be indicated by the networkdevice by using signaling, and the value of L₁ being a value of aparameter or a calculation formula of L₁ may be defined in a protocol.For example, the value of L₁ being a quantity N_(S) of antenna ports inone polarization direction, or the calculation formula of L₁, forexample, L₁=

N_(s)/2

, L₁=

N_(s)/2

, or L₁=[N_(s)/2], may be defined in the protocol. In this case, thevalue of L₁ may be understood as being implicitly indicated by usingindication information used to indicate a quantity of antenna ports in asingle polarization direction.

It should be understood that the foregoing enumerated values andcalculation formulas of L₁ or K₁ that are defined in the protocol aremerely examples, and should not constitute any limitation on thisapplication.

Optionally, the value of either L₁ or K₁ may be predefined, for example,defined in a protocol, and the value of the other one of L₁ and K₁ isdetermined by the terminal device and reported by the terminal device byusing signaling.

The foregoing has described in detail the process of determining L₁ andK₁ with reference to the manner of definition in the protocol and themanner of indication by the network device. A process of determining L₁and K₁ with reference to a manner of definition in a protocol and amanner of indication by the terminal device is similar. For brevity,details are not described herein again.

Because one of L₁ and K₁ may be defined in a protocol or may be definedas a value of a parameter in a protocol, or a calculation formula of L₁and K₁ may be defined in a protocol, the second indication informationmay be used to indicate a value of the other one of L₁ and K₁. Forexample, the value of K₁ is defined in the protocol, and the secondindication information is used to indicate only the value of L₁.Alternatively, the value of L₁ is defined in the protocol, and thesecond indication information is used to indicate only the value of K₁.

Because L₁, K₁, and M₁ satisfy M₁=L₁×K₁, when values of any two of L₁,K₁, and M₁ are determined, the value of the other one can also bedetermined. For example, when K₁ is defined in a protocol, the secondindication information may also be used to indirectly indicate the valueof L₁ by indicating a value of M₁. When L₁ is defined in a protocol, thesecond indication information may also be used to indirectly indicatethe value of K₁ by indicating a value of M₁.

It should be understood that the foregoing enumerated signaling used tocarry the second indication information is merely an example, and shouldnot constitute any limitation on this application. Specific signalingthat carries the second indication information is not limited in thisapplication.

If the value of T₁ is indicated by the network device, optionally, themethod further includes: The terminal device receives third indicationinformation, where the third indication information is used to indicatethe value of T₁. Correspondingly, the network device sends the thirdindication information.

Optionally, the third indication information is carried in higher layersignaling, for example, an RRC message.

If the value of T₁ is determined and reported by the terminal device,optionally, the method further includes: The terminal device sends thirdindication information, where the third indication information is usedto indicate the value of T₁. Correspondingly, the network devicereceives the third indication information.

Optionally, the third indication information is carried in UCI, forexample, CSI.

It should be understood that the foregoing enumerated signaling used forthe third indication information is merely an example, and should notconstitute any limitation on this application. Specific signaling thatcarries the third indication information is not limited in thisapplication.

It should be further understood that the second indication informationand the third indication information may be same information, or may bedifferent information. This is not limited in this application.

After determining the values of L₁, K₁, and T₁, the terminal device maydetermine the L₁ beam vectors, the K₁ frequency domain vectors, and theT₁ space-frequency component matrices, to generate the first indicationinformation.

Optionally, the first indication information is used to indicate L₁ beamvectors and T₁ space-frequency component matrices, and a weighted sum ofthe T₁ space-frequency component matrices is used to determine aprecoding vector of one or more frequency domain units. The L₁ beamvectors and K₁ frequency domain vectors correspond to M₁ space-frequencycomponent matrices, the T₁ space-frequency component matrices are a partof the M₁ space-frequency component matrices, each of the M₁space-frequency component matrices is uniquely determined by one of theL₁ beam vectors and one of the K₁ frequency domain vectors, andM₁=L₁×K₁; the L₁ beam vectors are a part of beam vectors in a beamvector set, and/or the K₁ frequency domain vectors are a part offrequency domain vectors in the frequency domain vector set; and M₁, L₁,K₁, and T₁ are all positive integers.

Optionally, the K₁ frequency domain vectors are preconfigured. Forexample, the K₁ frequency domain vectors may be all or a part offrequency domain vectors in the frequency domain vector set.

For example, K₁=K₀ may be predefined in the protocol. That is, in theprotocol, a universal set of the frequency domain vector set is used asthe K₁ frequency domain vectors by default. For another example, thevalue of K₁ may be predefined in the protocol, and frequency domainvectors in the frequency domain vector set that are used as the K₁frequency domain vectors may be specified in advance. For still anotherexample, the value of K₁ may be predefined in the protocol, and the K₁frequency domain vectors may be indicated by the network device inadvance by using signaling.

In other words, it may be predefined in the protocol that the terminaldevice does not need to report the K₁ frequency domain vectors. The K₁frequency domain vectors may be specified in advance, for example,defined in a protocol or configured by the network device. This is notlimited in this application.

Optionally, it may also be predefined in the protocol that the terminaldevice determines, based on different values of parameters, a vectorthat needs to be reported.

As described above, L₀>L₁, K₀>K₁, and L₀, L₁, K₀, and K₁ do not satisfyL₀=L₁ and K₀=K₁ at the same time. The L₁ beam vectors may be a universalset of the beam vector set, or the K₁ frequency domain vectors may be auniversal set of the frequency domain vector set. Optionally, theterminal device may determine, based on the values of L₁ and K₁, whetherto select the universal set of the beam vector set or the universal setof the frequency domain vector set. When the L₁ beam vectors are theuniversal set of the beam vector set, the terminal device may not reportthe L₁ beam vectors. When the K₁ frequency domain vectors are theuniversal set of the frequency domain vector set, the terminal devicemay not report the K₁ frequency domain vectors.

In an implementation, the network device may configure the value of K₁by using signaling, for example, the second indication information. WhenK₁ is configured to be equal to K₀, the terminal device may use theuniversal set of the frequency domain vector set as the K₁ frequencydomain vectors by default. Alternatively, the network device may notindicate the value of K₁ by using additional signaling. For example,only the value of L₁ is indicated in the second indication information.In other words, optionally, the second indication information is used toindicate the value of L₁. This may be understood as that the networkdevice implicitly indicates, by using the second indication information,that the value of K₁ is K₀.

The terminal device may determine, based on the received signaling,whether to report the K₁ frequency domain vectors. For example, when itis determined that K₁=K₀, the K₁ frequency domain vectors may not bereported. Alternatively, when determining that K₁=K₀, the network devicemay directly use frequency domain vectors in the frequency domain vectorset as the K₁ frequency domain vectors.

In another implementation, the value of K₁ may be defined in a protocolas a fixed value. When the value of K₁ is defined as K₀, the terminaldevice may use the universal set of the frequency domain vector set asthe K₁ frequency domain vectors by default, and does not need to reportthe K₁ frequency domain vectors.

Similarly, in an implementation, the network device may configure thevalue of L₁ by using signaling, for example, the second indicationinformation. When L₁ is configured to be equal to L₀, the terminaldevice may use the universal set of the beam vector set as the L₁ beamvectors by default. Alternatively, the network device may not indicatethe value of L₁ by using additional signaling. For example, only thevalue of K₁ is indicated in the second indication information. In otherwords, optionally, the second indication information is used to indicatethe value of K₁. In this case, this may be understood as that thenetwork device implicitly indicates, by using the second indicationinformation, that the value of L₁ is L₀.

The terminal device may determine, based on the received signaling,whether to report the L₁ beam vectors. For example, when it isdetermined that L₁=L₀, the L₁ beam vectors may not be reported.Alternatively, when determining that L₁=L₀, the network device maydirectly use beam vectors in the beam vector set as the L₁ beam vectors.

In another implementation, the value of L₁ may be defined in a protocolas a fixed value. When the value of L₁ is defined as L₀, the terminaldevice may use the universal set of the beam vector set as the L₁ beamvectors by default, and does not need to report the L₁ beam vectors.

Further, when the values of L₁, K₁, and T₁ are all configured by thenetwork device, the terminal device may determine, based on a parameterconfigured by the network device, a vector that needs to be reported.Optionally, it may alternatively be predefined in the protocol that theterminal device determines, based on different parameters configured bythe network device, a vector that needs to be reported.

For example, if the network device indicates the values of L₁, K₁, andT₁ by using signaling, the terminal device may report the L₁ beamvectors, the K₁ frequency domain vectors, and the T₁ space-frequencyvector pairs by default. If the network device indicates the values ofL₁ and T₁ by using signaling, the terminal device may consider K₁=K₀ bydefault. To be specific, all K₀ frequency domain vectors in thefrequency domain vector set may be used as the K₁ frequency domainvectors. The terminal device may report only the L₁ beam vectors and theT₁ space-frequency vector pairs. If the network device indicates thevalues of K₁ and T₁ by using signaling, the terminal device may considerL₁=L₀ by default. To be specific, all L₀ beam vectors in the beam vectorset may be used as the L₁ beam vectors. The terminal device may reportonly the K₁ frequency domain vectors and the T₁ space-frequency vectorpairs. If the network device indicates the values of L₁ and K₁ by usingsignaling, the terminal device may directly perform weighted summationon the L₁ beam vectors and the K₁ frequency domain vectors by default,may report only the L₁ beam vectors and the K₁ frequency domain vectors,and does not need to report the T₁ space-frequency vector pairs.

It should be understood that the foregoing lists vectors that need to bedetermined and reported by the terminal device when the network deviceconfigures different parameters. However, this should not constitute anylimitation on this application.

The following uses an example in which L₁≠L₀ and K₁≠K₀ to describe indetail a specific method for determining and indicating, by the terminaldevice, the T₁ space-frequency component matrices and the weights of thespace-frequency component matrices.

The terminal device may determine the T₁ space-frequency componentmatrices in a corresponding implementation based on a prestored vectorset. For example, the terminal device may prestore a beam vector set anda frequency domain vector set, and determine the T₁ space-frequencyvector pairs based on Implementation 1. Alternatively, the terminaldevice may prestore a space-frequency component matrix set, anddetermine the T₁ space-frequency component matrices based onImplementation 2.

It should be noted that the beam vector set and the frequency domainvector set may be converted into the space-frequency component matrixset, or vice versa. Any beam vector in the beam vector set and anyfrequency domain vector in the frequency domain vector set may be usedto obtain one space-frequency component matrix in the space-frequencycomponent matrix set. Any space-frequency component matrix in thespace-frequency component matrix set may be uniquely determined by onebeam vector in the beam vector set and one frequency domain vector inthe frequency domain vector set.

Therefore, an index corresponding to each space-frequency vector matrixin the space-frequency vector matrix set may also be converted into anindex of a beam vector in the beam vector set and an index of afrequency domain vector in the frequency domain vector set. In otherwords, any space-frequency component matrix in the space-frequencyvector matrix set may be indicated jointly by using one beam vector inthe beam vector set and one frequency domain vector in the frequencydomain vector set.

In this embodiment, the terminal device may indicate the T₁space-frequency component matrices by using at least the L₁ beam vectorsin the beam vector set and the K₁ frequency domain vectors in thefrequency domain vector set in either of the following implementations:

Implementation 1: The T₁ space-frequency component matrices may bedetermined by M₁ space-frequency vector pairs, and the M₁space-frequency vector pairs may be obtained by combining the L₁ beamvectors and the K₁ frequency domain vectors. The terminal device mayindicate, in the M₁ space-frequency vector pairs, T₁ space-frequencyvector pairs used to generate the T₁ space-frequency component matrices.

Implementation 2: The T₁ space-frequency component matrices may beselected from M₁ space-frequency component matrices, and the M₁space-frequency component matrices may be determined by the L₁ beamvectors and the K₁ frequency domain vectors. The terminal device mayindicate the T₁ space-frequency component matrices in the M₁space-frequency component matrices. It should be noted that manners ofprestoring a vector set or a matrix set by the terminal device and thenetwork device are not limited in this application. For example, boththe terminal device and the network device may prestore the beam vectorset and the frequency domain vector set. Alternatively, both theterminal device and the network device may prestore the space-frequencycomponent matrix set. Alternatively, the terminal device may prestorethe beam vector set and the frequency domain vector set, and the networkdevice may prestore the space-frequency component matrix set.Alternatively, the terminal device may prestore the space-frequencycomponent matrix set, and the network device may prestore the beamvector set and the frequency domain vector set.

Because the beam vector set and the frequency domain vector set may beconverted into the space-frequency component matrix set, or vice versa,when the space-frequency component matrix set and the beam vector setare determined, the frequency domain vector set may be deduced; or whenthe space-frequency component matrix set and the frequency domain vectorset are determined, the beam vector set may be deduced. Therefore,specific forms of the vector set prestored by the terminal device andthe network device are not limited in this application.

For ease of understanding of the embodiments of this application, in thefollowing descriptions, a specific process in which the terminal devicegenerates the first indication information is described with referenceto the specific form of the vector set or the matrix set and based onthe two implementations listed above.

Implementation 1

The terminal device may determine the M₁ space-frequency vector pairsbased on a prestored beam vector set, a prestored frequency domainvector set, and a predetermined space-frequency matrix, to determine theT₁ space-frequency component matrices.

It is assumed that precoding vectors of N_(f) frequency domain unitsdetermined by the terminal device are denoted as h₀, h₁, . . . , andh_(N) _(f) −1. The precoding vectors of the N_(f) frequency domain unitsmay be used to construct a space-frequency matrix H, where H

[h₀ h₁ . . . h_(N) _(f) ⁻¹], or H

[h₀ ^(T) h₁ ^(T) . . . h_(N) _(f) ⁻¹ ^(T)]^(T).

It should be noted that the two forms of the space-frequency matrixlisted above may be mutually converted. The terminal device maydetermine, based on a prestored vector set, a form of a space-frequencymatrix that needs to be constructed, to generate a space-frequencymatrix in a corresponding form. For example, when the terminal deviceprestores a beam vector set and a frequency domain vector set, aspace-frequency matrix H=[h₀ h₁ . . . h_(N) _(f) ⁻¹] may be generated.When the terminal device prestores a space-frequency component matrixset, a space-frequency matrix H=[h₀ ^(T) h₁ ^(T) . . . h_(N) _(f) ⁻¹^(T)]^(T) may be generated.

In this embodiment, the terminal device may construct, based on theprecoding vectors of the N_(f) frequency domain units, thespace-frequency matrix H having a dimension of N_(s)×N_(f), where H

[h₀ h₁ . . . h_(N) _(f) ⁻¹].

In a possible design, a beam vector set may include N_(s) beam vectors.That is, L₀=N_(s). A dimension of each beam vector may be N_(s), andeach beam vector may be obtained from a two-dimensional (2 dimension,2D)-DFT matrix. 2D may represent two different directions, for example,a horizontal direction and a vertical direction.

For example, the N_(s) beam vectors may be denoted as b_(s,0), b_(s,1),. . . , and b_(s,N) _(s) ⁻¹. A matrix B_(s) may be constructed by usingthe L₀ beam vectors, where B_(s)

[b_(s,0) b_(s,1) . . . b_(s, N) _(s) ⁻¹].

In another possible design, a beam vector set may be extended toO_(s)×N_(s) beam vectors by using an oversampling factor O_(s). In thiscase, the beam vector set may include O_(s) subsets, and each subset mayinclude N_(s) beam vectors. That is, L₀=O_(s)×N_(s). A dimension of eachbeam vector in the beam vector set may be N_(s), and each beam vectormay be obtained from an oversampled 2D-DFT matrix. The oversamplingfactor O_(s) is a positive integer. Specifically, O_(s)=O₁×O₂, O₁ may bean oversampling factor in a horizontal direction, and O₂ may be anoversampling factor in a vertical direction. O₁≥1, O₂≥1, and O₁ and O₂cannot be 1 at the same time and are both integers.

For example, N_(s) beam vectors in an o_(s) ^(th) (0≤o_(s)≤O_(s)−1, ando_(s) is an integer) subset of the beam vector set may be denoted asb_(s,0) ^(o) ^(s) , b_(s,1) ^(o) ^(s) , . . . , and b_(s,N) _(s) ⁻¹ ^(o)^(s) . In this case, a matrix B_(s) ^(o) ^(s) may be constructed basedon the N_(s) beam vectors in the o_(s) ^(th) subset, where B_(s) ^(o)^(s)

[b_(s,0) ^(o) ^(s) b_(s,1) ^(o) ^(s) . . . b_(s,N) _(s) ⁻¹ ^(o) ^(s) ].

In a possible design, a frequency domain vector set may include N_(f)frequency domain vectors. That is, K₀=N_(f). A dimension of eachfrequency domain vector may be N_(f), and each frequency domain vectormay be obtained from a DFT matrix.

For example, the N_(f) frequency domain vectors may be denoted asb_(f,0), b_(f,1), . . . , and b_(f, N) _(f) ⁻¹. A matrix B_(f) may beconstructed based on the N_(f) frequency domain vectors, where B_(f)

[b_(f,0) b_(f,1) . . . b_(f,N) _(f) ⁻¹].

In another possible design, a frequency domain vector set may beextended to O_(f)×N_(f) frequency domain vectors by using anoversampling factor O_(f). In this case, the frequency domain vector setmay include O_(f) subsets, and each subset may include N_(f) frequencydomain vectors. That is, K₀=O_(f)×N_(f). A dimension of each frequencydomain vector in the frequency domain vector set may be N_(f), and eachfrequency domain vector may be obtained from an oversampled DFT matrix.The oversampling factor O_(f) is a positive integer.

For example, N_(f) frequency domain vectors in an o_(f) ^(th)(0≤o_(f)≤O_(f)−1, and o_(s) is an integer) subset in the frequencydomain vector set may be denoted as b_(f,0) ^(o) ^(f) , b_(f,1) ^(o)^(f) , . . . , and b_(f,N) _(f) ⁻¹ ^(o) ^(f) . In this case, a matrixB_(f) ^(o) ^(f) may be constructed based on the N_(f) beam vectors inthe o_(f) ^(th) subset, where B_(f) ^(o) ^(f)

[b_(f,0) ^(o) ^(f) b_(f,1) ^(o) ^(f) . . . b_(f,N) _(f) ⁻¹ ^(o) ^(f) ].

The following separately describes specific methods for determining andindicating, by the terminal device, the T₁ space-frequency componentmatrices and the weighting coefficients of the space-frequency componentmatrices when an oversampling rate is considered and when theoversampling rate is not considered.

If the oversampling rate is not considered, the terminal device maydetermine the T₁ space-frequency component matrices and the weightingcoefficients of the space-frequency component matrices by using step 1-ito step 1-v shown below.

Step 1-i: The terminal device may determine a weighting coefficientmatrix based on the space-frequency matrix H, a matrix constructed basedon the beam vector set, and a matrix constructed based on the frequencydomain vector set.

If the oversampling rate is not considered, the beam vector set mayinclude N_(S) beam vectors, and the constructed matrix is B_(s); thefrequency domain vector set may include N_(f) frequency domain vectors,and a constructed matrix is BR. The terminal device may determine amatrix W by using W=B_(s)*HB_(f). The matrix W may be referred to as aweighting coefficient matrix, and a dimension of the weightingcoefficient matrix may be N_(s)×N_(f). N_(S) rows in the matrix W maycorrespond to the N_(s) beam vectors in the beam vector set (or thematrix B_(s) constructed by using the beam vector set). N_(f) columns inthe matrix W may correspond to the N_(f) frequency domain vectors in thefrequency domain vector set (or the matrix B_(f) constructed based onthe frequency domain vector set). Each coefficient in the matrix maycorrespond to one space-frequency vector pair.

Step 1-ii: The terminal device may select L₁ relatively strong beamvectors from the beam vector set, and select K₁ relatively strongfrequency domain vectors from the frequency domain vector set.

The terminal device may separately perform modulo operations on theN_(s) rows in the matrix W, and determine L₁ rows with relatively largemoduli according to a modulus of each row. Row numbers of the L₁ rows inthe matrix W may be sequence numbers of the L₁ relatively strong beamvectors in the beam vector set or column numbers of the L₁ relativelystrong beam vectors in B_(s). Further, the terminal device mayseparately perform modulo operations on the N_(f) columns in the matrixW, and determine K₁ columns with relatively large moduli according to amodulus of each column. The column numbers of the K₁ columns in thematrix W may be sequence numbers of the K₁ relatively strong frequencydomain vectors in the frequency domain vector set or column numbers ofthe K₁ relatively strong frequency domain vectors in B_(f).

It should be understood that the foregoing described specific methodused by the terminal device to determine the L₁ relatively strong rowsin the beam vector set and the K₁ relatively strong columns in thefrequency domain vector set is merely an example for ease ofunderstanding, and should not constitute any limitation on thisapplication. For a specific method used by the terminal device todetermine the L₁ relatively strong rows in the beam vector set and theK₁ relatively strong columns in the frequency domain vector set, referto the current technology. For brevity, details are not describedherein.

It should be further understood that the foregoing method fordetermining the L₁ beam vectors and the K₁ frequency domain vectors byusing the weighting coefficient matrix is merely a possibleimplementation shown for ease of understanding, but this does notindicate that the terminal device definitely generates the weightingcoefficient matrix when determining the L₁ beam vectors and the K₁frequency domain vectors. For example, a precoding vector of eachfrequency domain unit is separately projected to each beam vector in thebeam vector set and each frequency domain vector in the frequency domainvector set, to obtain an array set including a plurality of projectionvalues. Elements in the array set may be obtained by sequentiallyconnecting elements in rows (or columns) in the foregoing weightingcoefficient matrix.

Step 1-iii: The terminal device may obtain M₁ space-frequency vectorpairs by combining the L₁ relatively strong beam vectors determined inthe beam vector set and the K₁ relatively strong frequency domainvectors determined in the frequency domain vector set.

Each of the M₁ space-frequency vector pairs may include one beam vectorand one frequency domain vector. The beam vector in each space-frequencyvector pair may be obtained from the foregoing L₁ beam vectors, and thefrequency domain vector in each space-frequency vector pair may beobtained from the foregoing K₁ frequency domain vectors. One of the L₁beam vectors and one of the K₁ frequency domain vectors may be combinedto obtain a unique space-frequency vector pair. In other words, each ofthe M₁ space-frequency vector pairs is uniquely determined by one of theL₁ beam vectors and one of the K₁ frequency domain vectors. Any twospace-frequency vector pairs have a difference in at least one ofincluded beam vectors and frequency domain vectors. Therefore, L₁×K₁space-frequency vector pairs may be determined by the L₁ beam vectorsand the K₁ frequency domain vectors. That is, M₁=L₁×K₁.

On the other hand, the N_(s) beam vectors in the beam vector set and theN_(f) frequency domain vectors in the frequency domain vector set may becombined to obtain N_(S)×N_(f) space-frequency vector pairs. Therefore,the M₁ space-frequency vector pairs may be considered as a subset of theN_(S)×N_(f) space-frequency vector pairs, and M₁<N_(S)×N_(f). In otherwords, the terminal device may determine, in a subset of aspace-frequency vector pair set that is obtained by combining the beamvector set and the frequency domain vector set, T₁ space-frequencyvector pairs used for linear weighting, that is, T₁ space-frequencyvector pairs that need to be reported by the terminal device. In otherwords, the selected T₁ space-frequency vector pairs are selected fromthe M₁ space-frequency vector pairs obtained by combining the L₁ beamvectors and the K₁ frequency domain vectors.

Step 1-iv: The terminal device may determine the T₁ space-frequencyvector pairs in the M₁ space-frequency vector pairs. The T₁space-frequency vector pairs may be used to determine the T₁space-frequency component matrices.

The terminal device may select T₁ relatively strong space-frequencyvector pairs from the M₁ space-frequency vector pairs, to generate theT₁ space-frequency component matrices. The T₁ relatively strongspace-frequency vector pairs may be space-frequency vector pairs whoseweighting coefficients have relatively large moduli in the M₁space-frequency vector pairs. That is, a modulus of a weightingcoefficient of any one of the selected T₁ space-frequency vector pairsis greater than or equal to a modulus of a weighting coefficient of anyone of remaining M₁-T₁ space-frequency vector pairs.

Based on the L₁ relatively strong rows and the K₁ relatively strongcolumns in the matrix W determined in the foregoing descriptions, theterminal device may determine L₁×K₁ (that is, M₁) weightingcoefficients. The M₁ weighting coefficients may be in a one-to-onecorrespondence with the M₁ space-frequency vector pairs. The terminaldevice may determine T₁ weighting coefficients with relatively largermoduli in the M₁ weighting coefficients. A modulus of any one of theselected T₁ weighting coefficients is greater than or equal to a modulusof any one of remaining M₁-T₁ weighting coefficients. The T₁ weightingcoefficients may be weighting coefficients of the T₁ space-frequencycomponent matrices.

Locations of the T₁ weighting coefficients in the L₁×K₁ weightingcoefficients may be used to determine T₁ beam vectors and T₁ frequencydomain vectors included in the T₁ space-frequency vector pairs.

In an implementation, the terminal device may extract, from the matrixW, the L₁ rows with relatively large moduli and the K₁ columns withrelatively large moduli, to obtain a matrix having a dimension of L₁×K₁.For ease of differentiation and description, the matrix having thedimension of L₁×K₁ is denoted as W′. The matrix W′ may be considered asa submatrix of the matrix W. The terminal device may perform a modulooperation on each element in the matrix W′, to select T₁ elements withrelatively large moduli. Locations of the T₁ elements in the matrix W′may be used to determine locations, in the L₁ beam vectors, of the beamvectors included in the T₁ space-frequency vector pairs and locations,in the K₁ frequency domain vectors, of the frequency domain vectorsincluded in the T₁ space-frequency vector pairs. Specifically, rownumbers of the T₁ elements in the matrix W′ may be sequence numbers ofthe selected T₁ beam vectors in the L₁ beam vectors, and column numbersof the T₁ elements in the matrix W′ may be sequence numbers of theselected T₁ frequency domain vectors in the K₁ frequency domain vectors.

In another implementation, according to a predefined rule, for example,first rows and then columns or first columns and then rows, the terminaldevice may sequentially arrange the L₁ rows with relatively large moduliand the K₁ columns with relatively large moduli that are extracted fromthe matrix W, to obtain an array including the L₁×K₁ weightingcoefficients. The terminal device may perform a modulo operation on eachelement in the array, to select T₁ elements with relatively largemoduli. Locations of the T₁ elements in the array may be used todetermine locations, in the L₁ beam vectors, of the beam vectorsincluded in the T₁ space-frequency vector pairs and locations, in the K₁frequency domain vectors, of the frequency domain vectors included inthe T₁ space-frequency vector pairs.

The T₁ space-frequency vector pairs may be used to determine the T₁space-frequency component matrices. It is assumed that the T₁ beamvectors in the T₁ space-frequency vector pairs selected by the terminaldevice in step 1-iv are denoted as u_(s) ⁰, u_(s) ¹, . . . , and u_(s)^(T) ¹ ⁻¹, and that the T₁ frequency domain vectors in the T₁space-frequency vector pairs are denoted as u_(f) ⁰, u_(f) ¹, . . . ,and u_(f) ^(T) ¹ ⁻¹. A space-frequency component matrix may be U_(t) ₁ ,where U_(t) ₁ =u_(s) ^(t) ¹ (u_(f) ^(t) ¹ )* or U_(t) ₁ =u_(f) ^(t) ¹⊗u_(s) ^(t) ¹ , and t₁=0, 1, . . . , T₁−1. u_(s) ^(t) ¹ (u_(f) ^(t) ¹ )*may be a matrix having a dimension of N_(s)×N_(f), and u_(f) ^(t) ¹⊗u_(s) ^(t) ¹ may be a vector having a length of N_(s)×N_(f).

It should be understood that the terminal device does not necessarilygenerate the T₁ space-frequency component matrices based on the T₁space-frequency vector pairs described above. Herein, for ease ofunderstanding only, several possible manners of conversion between aspace-frequency vector pair and a space-frequency component matrix areshown.

Step 1-v: The terminal device generates the first indicationinformation, to indicate the L₁ beam vectors, the K₁ frequency domainvectors, and the T₁ space-frequency vector pairs.

Based on the L₁ beam vectors, the K₁ frequency domain vectors, and theT₁ space-frequency vector pairs that are determined in step 1-i to step1-iv, the first indication information may include location informationof the L₁ beam vectors in the beam vector set, location information ofthe K₁ frequency domain vectors in the frequency domain vector set, andinformation used to indicate the T₁ space-frequency vector pairs.

Optionally, when the first indication information is used to indicatethe L₁ beam vectors, the first indication information may be used toindicate an index of a combination of the L₁ beam vectors in the beamvector set. For example, a plurality of combinations of a plurality ofbeam vectors may be predefined in a protocol, and each combination maycorrespond to one index. The L₁ beam vectors may be one of the pluralityof combinations, or close to one of the plurality of combinations. Thefirst indication information may indicate the L₁ beam vectors byindicating an index of the combination. In other words, the locationinformation of the L₁ beam vectors in the beam vector set may be anindex of a combination of the L₁ beam vectors in the beam vector set. Inthis case, the terminal device may indicate the L₁ beam vectors in thebeam vector set by using log,

C_(N) _(s) ^(L) ¹

bits.

represents rounding up.

Optionally, when the first indication information is used to indicatethe K₁ frequency domain vectors, the first indication information may beused to indicate an index of a combination of the K₁ frequency domainvectors in the frequency domain vector set. For example, a plurality ofcombinations of a plurality of beam vectors may be predefined in aprotocol, and each combination may correspond to one index. The K₁frequency domain vectors may be one of the plurality of combinations, orclose to one of the plurality of combinations. The first indicationinformation may indicate the K₁ frequency domain vectors by indicatingan index of the combination. In other words, the location information ofthe K₁ frequency domain vectors in the frequency domain vector set maybe an index of a combination of the K₁ frequency domain vectors in thefrequency domain vector set. In this case, the terminal device mayindicate the K₁ frequency domain vectors in the frequency domain vectorset by using log₂

C_(N) _(f) ^(K) ¹

bits.

It should be understood that the method for indicating the L₁ beamvectors by indicating the index of the combination of the L₁ beamvectors and the method for indicating the K₁ frequency domain vectors byindicating the index of the combination of the K₁ frequency domainvectors are merely a possible implementation, and should not constituteany limitation on this application. For example, when the firstindication information is used to indicate the L₁ beam vectors, thefirst indication information may also be used to indicate an index ofeach of the L₁ beam vectors in the beam vector set; or when the firstindication information is used to indicate the K₁ frequency domainvectors, the first indication information may also be used to indicatean index of each of the K₁ frequency domain vectors in the frequencydomain vector set. Specific manners of indicating the L₁ beam vectorsand the K₁ frequency domain vectors are not limited in this application.

Optionally, the first indication information may be used to indicate theT₁ space-frequency vector pairs in any one of the following manners:

Manner 1: The T₁ space-frequency vector pairs in the M₁ space-frequencyvector pairs are indicated by using a bitmap (bitmap).

Manner 2: An index of a combination of the T₁ space-frequency vectorpairs in the M₁ space-frequency vector pairs is indicated.

Manner 3: A location, in the L₁ beam vectors, of a beam vectorcorresponding to each of the T₁ space-frequency vector pairs and alocation, in the K₁ frequency domain vectors, of a frequency domainvector corresponding to each of the T₁ space-frequency vector pairs areindicated.

Manner 4: A location, in the M₁ space-frequency vector pairs, of each ofthe T₁ space-frequency vector pairs is indicated.

With reference to the foregoing four manners, the following describes indetail a specific method for indicating the T₁ space-frequency vectorpairs by using the first indication information.

In the manner 1, the terminal device may indicate T₁ space-frequencyvector pairs in the M₁ space-frequency vector pairs by using an M₁-bitbitmap. Each bit in the bitmap may correspond to one of the M₁space-frequency vector pairs. Each bit may be used to indicate whether acorresponding space-frequency vector pair is selected as one of the T₁space-frequency vector pairs. Alternatively, each bit may be used toindicate whether a corresponding space-frequency vector pair belongs tothe T₁ space-frequency vector pairs. For example, when a bit is set to“0”, it indicates that a corresponding space-frequency vector pair doesnot belong to the T₁ space-frequency vector pairs. When a bit is set to“1”, it indicates that a corresponding space-frequency vector pairbelongs to the T₁ space-frequency vector pairs.

A correspondence between the M₁ bits in the bitmap and the M₁space-frequency vector pairs corresponds to a combination manner of abeam vector and a frequency domain vector in the M₁ space-frequencyvector pairs. For example, the M₁ space-frequency vector pairscorresponding to the M₁ bits may be arranged in an order of firsttraversing the K₁ frequency domain vectors and then traversing the L₁beam vectors, or may be arranged in an order of first traversing the L₁beam vectors and then traversing the K₁ frequency domain vectors.

It is assumed that the selected L₁ beam vectors in the beam vector setare denoted as v_(s) ⁰, v_(s) ¹, . . . , and v_(s) ^(L) ¹ ⁻¹, and theselected K₁ frequency domain vectors in the frequency domain vector setare denoted as v_(f) ⁰, v_(f) ¹, . . . , and v_(f) ^(K) ¹ ⁻¹.

If the K₁ frequency domain vectors are first traversed and the L₁ beamvectors are then traversed, an arrangement order of the M₁space-frequency vector pairs may be (v_(s) ⁰, v_(f) ⁰), (v_(s) ⁰, v_(f)¹), . . . , (v_(s) ⁰, v_(f) ^(K) ¹ ⁻¹), (v_(s) ¹, v_(f) ⁰), (v_(s) ¹,v_(f) ¹), . . . , and (v_(s) ^(L) ¹ ⁻¹, v_(f) ^(K) ¹ ⁻¹). There are atotal of M₁ space-frequency vector pairs. For brevity, examples are notfurther listed one by one herein. The M₁ bits in the bitmap are in aone-to-one correspondence with the M₁ space-frequency vector pairs.

A 0^(th) bit to a (K₁−1)^(th) bit in the M₁ bits in the bitmap are in aone-to-one correspondence with the space-frequency vector pairs (v_(s)⁰, v_(f) ⁰), (v_(s) ⁰, v_(f) ¹), . . . , and (v_(s) ⁰, v_(f) ^(K) ¹ ⁻¹).A K₁ ^(th) bit to a (2K₁−1)^(th) bit are in one-to-one correspondencewith the space-frequency vector pairs (v_(s) ¹, v_(f) ⁰), (v_(s) ¹,v_(f) ¹), . . . , and (v_(s) ¹, v_(f) ^(K) ¹ ⁻¹). By analogy, an[(L₁−1)×K₁]^(th) bit to an (L₁×K₁−1)^(th) bit are in a one-to- onecorrespondence with the space-frequency vector pairs (v_(s) ^(L) ¹ ⁻¹,v_(f) ⁰), (v_(s) ^(L) ¹ ⁻¹, v_(f) ¹), . . . , and (v_(s) ^(L) ¹ ⁻¹,v_(f) ^(K) ¹ ⁻¹).

If the L₁ beam vectors are first traversed and the K₁ frequency domainvectors are then traversed, an arrangement order of the M₁space-frequency vector pairs may be (v_(s) ⁰, v_(f) ⁰), (v_(s) ¹, v_(f)⁰), . . . , (v_(s) ^(L) ¹ ⁻¹, v_(f) ⁰), (v_(s) ⁰, v_(f) ¹), (v_(s) ¹,v_(f) ¹), . . . , and (v_(s) ^(L) ¹ ⁻¹, v_(f) ^(K) ¹ ⁻¹). There are atotal of M₁ space-frequency vector pairs. For brevity, examples are notlisted herein one by one. The M₁ bits in the bitmap are in a one-to-onecorrespondence with the M₁ space-frequency vector pairs.

A 0^(th) bit to an (L₁−1)^(th) bit in the M₁ bits in the bitmap are in aone-to-one correspondence with the space-frequency vector pairs (v_(s)⁰, v_(f) ⁰), (v_(s) ¹, v_(f) ⁰), . . . , and (v_(s) ^(L) ¹ ⁻¹, v_(f) ⁰).An L₁ ^(th) bit to an (2L₁−1)^(th) bit are in a one-to-onecorrespondence with the space-frequency vector pairs (v_(s) ⁰, v_(f) ¹),(v_(s) ¹, v_(f) ¹), . . . , and (v_(s) ^(L) ¹ ⁻¹, v_(f) ¹). By analogy,an [L₁×(K₁−1)]^(th) bit to an (L₁×K₁−1)^(th) bit are in one-to-onecorrespondence with the space-frequency vector pairs (v_(s) ⁰, v_(f)^(K) ¹ ⁻¹), (v_(s) ¹, v_(f) ^(K) ¹ ⁻¹), . . . , and (v_(s) ^(L) ¹ ⁻¹,v_(f) ^(K) ¹ ⁻¹).

It should be understood that the foregoing enumerated one-to-onecorrespondence between the M₁ bits and the M₁ space-frequency vectorpairs is merely an example, and should not constitute any limitation onthis application. The correspondence between the M₁ bits and the M₁space-frequency vector pairs is not limited in this application. Inaddition, an arrangement manner of the M₁ space-frequency vector pairsis not limited in this application. The foregoing shows two possiblearrangement manners of the M₁ space-frequency vector pairs that are inthe one-to-one correspondence with the M₁ bits, merely for ease ofdescribing the one-to-one correspondence between the M₁ bits and the M₁space-frequency vector pairs.

In the manner 2, the terminal device may indicate the T₁ space-frequencyvector pairs by using the index of the combination of the T₁space-frequency vector pairs in the M₁ space-frequency vector pairs. Inother words, the terminal device may predetermine a plurality ofcombinations of a plurality of space-frequency vector pairs based on theM₁ space-frequency vector pairs obtained by combining the L₁ beamvectors and the K₁ frequency domain vectors. Each combination maycorrespond to one index. The T₁ space-frequency vector pairs may be oneof the plurality of combinations, or may be close to one of theplurality of combinations. The first indication information may indicatethe T₁ space-frequency vector pairs by indicating an index of thecombination. Therefore, the terminal device may indicate the T₁space-frequency vector pairs in the M₁ space-frequency vector pairs byusing log₂

C_(M) ₁ ^(T) ¹

bits.

In the manner 3, the terminal device may separately indicate thelocations of the T₁ beam vectors in the L₁ beam vectors and thelocations of the T₁ frequency domain vectors in the K₁ frequency domainvectors, where the T₁ beam vectors and the T₁ frequency domain vectorsare combined to obtain the T₁ space-frequency vector pairs. The terminaldevice may indicate a location of each beam vector in the L₁ beamvectors by using

log₂ L₁

bits, and the terminal device may indicate a location of each frequencydomain vector in the K₁ frequency domain vectors by using

log₂ K₁

bits.

In the manner 4, the terminal device may indicate the location of eachof the T₁ space-frequency vector pairs in the M₁ space-frequency vectorpairs. Herein, the location of each space-frequency vector pair in theM₁ space-frequency vector pairs may be understood as a relativelocation, or a local (local) location, of each space-frequency vectorpair in the M₁ space-frequency vector pairs. For example, the terminaldevice may indicate an index of each space-frequency vector pair in theM₁ space-frequency vector pairs. In this case, the terminal device mayindicate the index of the space-frequency vector pair in the M₁space-frequency vector pairs by using

log₂ M₁

bits.

In the several manners listed above, the space-frequency vector pair maybe represented in a form of a space-frequency component matrix(including a matrix form or a vector form), or may be represented in aform of a vector pair obtained by combining a beam vector and afrequency domain vector. This is not limited in this application.

It can be learned that in the foregoing listed methods for indicating T₁space-frequency vector pairs, the terminal device indicates the T₁space-frequency vector pairs by using relative locations (for example,relative indexes or relative numbers) of the T₁ space-frequency vectorpairs in the M₁ space-frequency vector pairs, or indicates the T₁space-frequency vector pairs by using relative locations (for example,relative indexes or relative numbers) of the T₁ space-frequency vectorpairs in the L₁ beam vectors and the K₁ frequency domain vectors.Because a selection range is narrowed, overheads caused by indicatingthe T₁ space-frequency vector pairs are also reduced.

It should be understood that the foregoing enumerated methods forindicating the T₁ space-frequency vector pairs are merely examples, andshould not constitute any limitation on this application. For example, aquantity of space-frequency vector pairs corresponding to each beamvector is K₁; in L₁×K₁ space-frequency vector pairs corresponding to theL₁ beam vectors, the terminal device may report, based on each beamvector, a space-frequency component pair that is selected for weightedsummation to determine a precoding vector. For example, if quantities ofselected space-frequency vector pairs that are in the space-frequencyvector pairs and that correspond to the beam vectors are the same, thatis, are T₁/L₁, the terminal device may indicate, based on each beamvector, an index of a combination of the T₁/L₁ selected space-frequencyvector pairs in the K₁ space-frequency vector pairs corresponding to thesame beam vector. If quantities of selected space-frequency vector pairsthat are in the K₁ space-frequency vector pairs and that correspond tothe beam vectors are different from each other, the terminal device mayreport a quantity of selected space-frequency vector pairs based on eachbeam vector, and an index of a combination of the selectedspace-frequency vector pairs in the K₁ space-frequency vector pairscorresponding to the same beam vector.

It should be understood that the method for indicating the T₁space-frequency vector pairs by the terminal device is not limited tothe foregoing listed methods in this application. For brevity, examplesare not further listed one by one herein. A specific method forindicating the T₁ space-frequency vector pairs by the terminal device isnot limited in this application.

Optionally, the first indication information further includesquantization information of the weighting coefficients of the T₁space-frequency vector pairs.

The terminal device may generate the quantization information of theweighting coefficients of the T₁ space-frequency vector pairs based onthe weighting coefficients of the T₁ space-frequency vector pairs thatare determined in step 1-iv.

Optionally, the terminal device may indicate, based on the weightingcoefficients of the T₁ space-frequency vector pairs determined in step1-iv, the T₁ weighting coefficients through normalization.

Specifically, the terminal device may determine a weighting coefficient(for example, denoted as a maximum weighting coefficient) with a maximummodulus in the T₁ weighting coefficients, and indicate a location of themaximum weighting coefficient in the matrix W′. Then, the terminaldevice may further indicate a relative value of each of remaining T₁−1weighting coefficients relative to the maximum weighting coefficient.For example, the terminal device may indicate the remaining T₁−1weighting coefficients by using an index of a quantized value of eachrelative value. For example, a one-to-one correspondence between aplurality of quantized values and a plurality of indexes may bepredefined in a codebook, and the terminal device may feed back therelative values of the weighting coefficients relative to the maximumweighting coefficient to the network device based on the one-to-onecorrespondence. Therefore, the weighting coefficient fed back by theterminal device may be the same as or similar to the weightingcoefficient determined in step 1-iv, and therefore is referred to as aquantized value of the weighting coefficient. Information used toindicate the quantized value of the weighting coefficient may bereferred to as quantized information of the weighting coefficient. Thequantized information may be, for example, the index of the quantizedvalue.

It should be understood that indicating the weighting coefficientsthrough normalization is merely a possible implementation, and shouldnot constitute any limitation on this application. For a specific methodfor indicating the weighting coefficient by the terminal device, referto a method in the current technology. For brevity, details are notdescribed herein.

It should be noted that the normalization mentioned herein may bedetermining a maximum weighting coefficient based on each polarizationdirection, each transport layer, or all transport layers, so thatnormalization is performed in different ranges such as each polarizationdirection, each transport layer, or all transport layers.

It should be further understood that the foregoing methods fordetermining the L₁ beam vectors, the K₁ frequency domain vectors, the T₁space-frequency vector pairs, and the weighting coefficients of thespace-frequency vector pairs by the terminal device are merely examples,and should not constitute any limitation on this application.

For example, optionally, the terminal device may alternatively determineand feed back a wideband amplitude coefficient for each of the L₁ beamvectors. In this case, the first indication information may furtherinclude quantization information of wideband amplitude coefficients ofthe L₁ beam vectors.

Optionally, the terminal device may first select the L₁ beam vectors,then select K₁ frequency domain vectors for each beam vector, andfurther determine weighting coefficients corresponding tospace-frequency vectors including each beam vector and a frequencydomain vector corresponding to the beam vector. That is, there are atotal of L₁×K₁ weighting coefficients.

In this case, the first indication information is specifically used toindicate each beam vector in the L₁ beam vectors and a frequency domainvector corresponding to each beam vector. The possible design may beapplied to a scenario in which at least two of the selected L₁ beamvectors correspond to different frequency domain vectors, andparticularly, may be applied to a scenario in which at least two of theselected L₁ beam vectors correspond to different frequency domainvectors and a relatively small quantity of beam vectors are selected, orin other words, a value of L₁ is relatively small (that is, spatialsparsity is relatively good). Optionally, the first indicationinformation is further used to indicate a quantity of frequency domainvectors corresponding to each beam vector. Optionally, at least two beamvectors correspond to different quantities of frequency domain vectors.

If a frequency domain vector is selected for each beam vector, andfrequency domain vectors selected for at least two beam vectors aredifferent, after determining the T₁ space-frequency vector pairs in theM₁ space-frequency vector pairs, the terminal device may separatelyindicate the selected space-frequency vector pairs based on each beamvector. For example, based on each beam vector, the terminal device mayuse any one of the foregoing listed manner 1 to manner 4 for indication.

If at least two beam vectors correspond to different quantities offrequency domain vectors, when the terminal device uses the manner 2 forindication, the terminal device may further indicate the quantity offrequency domain vectors corresponding to each beam vector.

If quantities of selected space-frequency vector pairs in thespace-frequency vector pairs corresponding to the at least two beamvectors are different, when the terminal device uses the manner 2 forindication, the terminal device may further indicate a quantity ofselected space-frequency vector pairs in the space-frequency vectorpairs corresponding to each beam vector.

Optionally, the terminal device may alternatively first select Kfrequency domain vectors, then select L beam vectors for each frequencydomain vector, and further determine weighting coefficientscorresponding to space-frequency vector pair including each frequencydomain vector and a beam vector corresponding to the frequency domainvector. That is, there are a total of L×K weighting coefficients.

In this case, the first indication information is specifically used toindicate each frequency domain vector in the K frequency domain vectorsand a beam vector corresponding to each frequency domain vector. Thepossible design may be applied to a scenario in which beam vectorscorresponding to at least two of the selected K frequency domain vectorsare different, and particularly, may be applied to a scenario in whichbeam vectors corresponding to at least two of the selected K frequencydomain vectors are different and a relatively small quantity offrequency domain vectors are selected, or in other words, a value of Kis relatively small (that is, frequency domain sparsity is relativelygood). Optionally, the first indication information is further used toindicate a quantity of beam vectors corresponding to each frequencydomain vector. Optionally, at least two frequency domain vectorscorrespond to different quantities of beam vectors.

If a beam vector is selected for each frequency domain vector, and beamvectors selected for at least two frequency domain vectors aredifferent, after determining the T₁ space-frequency vector pairs in theM₁ space-frequency vector pairs, the terminal device may separatelyindicate the selected space-frequency vector pairs based on eachfrequency domain vector. For example, based on each frequency domainvector, the terminal device may use any one of the foregoing listedmanner 1 to manner 4 for indication.

If at least two frequency domain vectors correspond to differentquantities of beam vectors, when the terminal device uses the manner 2for indication, the terminal device may further indicate the quantity ofbeam vectors corresponding to each frequency domain vector.

If quantities of selected space-frequency vector pairs in thespace-frequency vector pairs corresponding to the at least two beamvectors are different, when the terminal device uses the manner 2 forindication, the terminal device may further indicate a quantity ofselected space-frequency vector pairs in the space-frequency vectorpairs corresponding to each beam vector.

In addition, as described above, the L₁ beam vectors may be some or allbeam vectors in the beam vector set, that is, L₁≤N_(s). The K₁ frequencydomain vectors may be some or all frequency domain vectors in thefrequency domain vector set, that is, K₁≤N_(f). However, L₁, K₁, N_(s),and N_(f) do not satisfy L₁=N_(s) and K₁=N_(f) at the same time.

When L₁=N_(s), the first indication information may indicate only the K₁frequency domain vectors and the T₁ space-frequency vector pairs, anddoes not indicate the L₁ beam vectors by using additional information.In other words, the first indication information is used to indicate theK₁ frequency domain vector pairs and the T₁ space-frequency vectorpairs. When the network device receives the first indicationinformation, it may be considered by default that the L₁ beam vectorsare a universal set of the beam vector set.

When K₁=N_(f), the first indication information may indicate only the L₁beam vectors and the T₁ space-frequency vector pairs, and does notindicate the K₁ frequency domain vectors by using additionalinformation. When the network device receives the first indicationinformation, it may be considered by default that the K₁ frequencydomain vectors are a universal set of the frequency domain vector set.

It should be further understood that the quantization information of theweighting coefficients of the T₁ space-frequency vector pairs may becarried in the first indication information, or may be carried inadditional information. This is not limited in this application.

If the oversampling rate is considered, there may be the following threepossible cases for vectors included in the beam vector set and thefrequency domain vector set:

Case 1: The beam vector set is extended to O_(s)×N_(s) beam vectors byusing an oversampling factor O_(s), and the frequency domain vector setis extended to O_(f)×N_(f) frequency domain vectors by using anoversampling factor O_(f).

Case 2: The beam vector set is extended to O_(s)×N_(s) beam vectors byusing an oversampling factor O_(s), and the frequency domain vector setincludes N_(f) frequency domain vectors.

Case 3: The beam vector set includes N_(s) beam vectors, and thefrequency domain vector set is extended to O_(f)×N_(f) frequency domainvectors by using an oversampling factor O_(f).

For the foregoing three possible cases, processing manners of theterminal device may be the same. The following uses the case 1 as anexample to describe in detail a specific process in which the terminaldevice determines the T₁ space-frequency component matrices and theweighting coefficients of the space-frequency component matrices.

The terminal device may specifically determine the T₁ space-frequencycomponent matrices and the weighting coefficients of the space-frequencycomponent matrices by using step 2-i to step 2-vi shown below.

Step 2-i: The terminal device may determine a weighting coefficientmatrix based on the space-frequency matrix H, a matrix constructed basedon the beam vector set, and a matrix constructed based on the frequencydomain vector set.

If the beam vector set is extended to O_(s)×N_(s) beam vectors by usingan oversampling factor O_(s), and the frequency domain vector set isextended to O_(f)×N_(f) frequency domain vectors by using anoversampling factor O_(f), the beam vector set may include O_(s)subsets, and a matrix B_(s) ^(o) ^(s) may be constructed based on ano_(s) ^(th) subset; the frequency domain vector set may include O_(f)subsets, and a matrix B_(f) ^(o) ^(f) may be constructed based on ano_(f) ^(th) subset. The terminal device may determine a matrix W_(o)_(s) _(,o) _(f) by using w_(o) _(s) _(,o) _(f) =(B_(s) ^(o) ^(s))*HB_(f) ^(o) ^(f) . The matrix W_(o) _(s) _(,o) _(f) , may beconsidered as a weighting coefficient matrix corresponding to the o_(s)^(th) subset and the o_(f) ^(th) subset, and a dimension of the matrixmay be N_(s)×N_(f). The N_(S) rows in the matrix W_(o) _(s) _(,o) _(f)may correspond to N_(s) beam vectors in the o_(s) ^(th) subset (or amatrix B_(s) ^(o) ^(s) constructed by the o_(s) ^(th) subset) in thebeam vector set. The N_(f) columns in the matrix W_(o) _(s) _(,o) _(f)may correspond to N_(f) frequency domain vectors in the o_(f) ^(th)subset (or a matrix B_(f) ^(o) ^(f) constructed based on the o_(f) ^(th)subset) in the frequency domain vector set. Each coefficient in thematrix W_(o) _(s) _(, o) _(f) may correspond to one space-frequencyvector pair.

Step 2-ii: The terminal device may determine O_(s)×O_(f) groups ofspace-frequency vector pairs based on the O_(s) subsets in the beamvector set and the O_(f) subsets in the frequency domain vector set,where each group of space-frequency vector pairs includes T₁space-frequency vector pairs.

Specifically, the terminal device may separately traverse 0 to O_(s)−1for a value of o_(s), traverse 0 to O_(f)−1 for a value of o_(f), andrepeatedly perform the following steps to determine the O_(s)×O^(f)groups of space-frequency vector pairs: determining L₁ relatively strongrows and K₁ relatively strong columns based on the matrix W_(o) _(s)_(,o) _(f) , and determining L₁ relatively strong beam vectors in theo_(s) ^(th) subset and K₁ relatively strong frequency domain vectors inthe o_(f) ^(th) subset. The L₁ beam vectors and the K₁ frequency domainvectors may be combined to obtain M₁ space-frequency vector pairs.Further, the terminal device may determine T₁ relatively strongspace-frequency vector pairs based on L₁×K₁ that is determined based onthe L₁ relatively strong rows and the K₁ relatively strong columns inthe matrix W_(o) _(s) _(,o) _(f) .

The specific process in which the terminal device determines the L₁relatively strong beam vectors and the K₁ relatively strong frequencydomain vectors based on the weighting coefficient matrix W, and thendetermines the T₁ relatively strong space-frequency vector pairs hasbeen described in detail in the foregoing step 1-ii to step 1-v. Forbrevity, details are not described herein again.

Step 2-iii: The terminal device may select a strongest group ofspace-frequency vector pairs based on the weighting coefficients of theO_(s)×O_(f) groups of space-frequency vector pairs, to determine the T₁space-frequency vector pairs and weighting coefficients of thespace-frequency vector pairs.

The terminal device may determine the strongest group of space-frequencyvector pairs based on the O_(s)×O_(f) groups of space-frequency vectorpairs determined in step 2-ii, where T₁ space-frequency vector pairs inthe strongest group of space-frequency vector pairs may be used togenerate the T₁ space-frequency component matrices. For example, theterminal device may separately calculate a sum of moduli of weightingcoefficients of each group of space-frequency vector pairs in theO_(s)×O_(f) groups of space-frequency vector pairs, and select a groupof space-frequency vector pairs whose sum of moduli is the largest, togenerate the T₁ space-frequency component matrices. Weightingcoefficient of the group of space-frequency vector pairs are theweighting coefficients of the T₁ space-frequency component matrices.

The specific process in which the terminal device generates the T₁space-frequency component matrices based on the T₁ space-frequencyvectors has been described in detail in the foregoing step 1-v. Forbrevity, details are not described herein again.

Because the T₁ beam vectors included in the T₁ space-frequency vectorpairs are from a same subset of the beam vector set, when determiningthe T₁ space-frequency vector pairs, the terminal device can alsodetermine the subset to which the T₁ beam vectors belong. In this way,L₁ relatively strong beam vectors in the subset can be determined.

Likewise, because the T₁ frequency domain vectors included in the T₁space-frequency vector pairs are from a same subset of the frequencydomain vector set, when determining the T₁ space-frequency vector pairs,the terminal device can also determine the subset to which the T₁frequency domain vectors belong. In this way, K₁ relatively strongfrequency domain vectors in the subset can be determined.

It should be understood that the foregoing method for determining the L₁beam vectors and the K₁ frequency domain vectors by using the weightingcoefficient matrix is merely a possible implementation shown for ease ofunderstanding, but this does not indicate that the terminal devicedefinitely generates the weighting coefficient matrix when determiningthe L₁ beam vectors and the K₁ frequency domain vectors. For example, aprecoding vector of each frequency domain unit is separately projectedto each beam vector in any subset of the beam vector set and eachfrequency domain vector in any subset of the frequency domain vectorset, to obtain an array set including a plurality of projection values.Elements in the array set may be obtained by sequentially connectingelements in rows (or columns) in the foregoing weighting coefficientmatrix.

Step 2-iv: The terminal device generates the first indicationinformation, to indicate the L₁ beam vectors, the K₁ frequency domainvectors, and the T₁ space-frequency vector pairs.

Based on the L₁ beam vectors, the K₁ frequency domain vectors, and theT₁ space-frequency vector pairs that are determined in step 2-i to step2-iii, the first indication information may include location informationof the L₁ beam vectors in the beam vector set, location information ofthe K₁ frequency domain vectors in the frequency domain vector set, andinformation used to indicate the T₁ space-frequency vector pairs.

Optionally, when the first indication information is used to indicatethe L₁ beam vectors, the first indication information may bespecifically used to indicate a subset to which the L₁ beam vectorsbelong and indexes of the L₁ beam vectors in the subset, or may bespecifically used to indicate a subset to which the L₁ beam vectorsbelong and an index of a combination of the L₁ beam vectors in thesubset.

Optionally, when the first indication information is used to indicatethe K₁ frequency domain vectors, the first indication information may bespecifically used to indicate a subset to which the K₁ frequency domainvectors belong and indexes of the K₁ frequency domain vectors in thesubset, or may be specifically used to indicate a subset to which the K₁frequency domain vectors belong and an index of a combination of the K₁frequency domain vectors in the subset.

When the first indication information is used to indicate the T₁space-frequency vector pairs, a specific indication manner may be anyone of the manner 1 to the manner 4 described above. The foregoing hasdescribed the manner 1 to the manner 4 in detail. For brevity, detailsare not described herein again.

Optionally, the first indication information further includesquantization information of the weighting coefficients of the T₁space-frequency vector pairs.

It should be understood that the quantization information of theweighting coefficients of the T₁ space-frequency vector pairs may becarried in the first indication information, or may be carried inadditional information. This is not limited in this application.

In the case 2, because the beam vector set is extended to theO_(s)×N_(s) beam vectors by using the oversampling factor O, and thefrequency domain vector set includes N_(f) frequency domain vectors, theterminal device may construct a matrix B_(s) ^(o) ^(s) (o_(s)=0, 1, . .. , O_(s)−1) and a matrix B_(f). Then, the terminal device may traverse0 to O_(s)−1 for a value of o_(s), and determine the T₁ space-frequencycomponent matrices and the weighting coefficients of the space-frequencycomponent matrices by using W_(o) _(s) =(B_(s) ^(o) ^(s) )*HB_(f).

In the case 3, because the beam vector set includes N_(f) frequencydomain vectors, and the frequency domain vector set is extended to theO_(f)×N_(f) frequency domain vectors by using the oversampling factorO_(f), the terminal device may construct a matrix B_(S) and a matrixB_(f) ^(o) ^(f) (o_(f)=0, 1, . . . , O_(f)−1). Then, the terminal devicemay traverse 0 to O_(f)−1 for a value of o_(f), and determine the T₁space-frequency component matrices and the weighting coefficients of thespace-frequency component matrices by using W_(o) _(f) =(B_(s))*HB_(f)^(o) ^(f) .

Specific methods for determining, by the terminal device, the T₁space-frequency component matrices and the weighting coefficients of thespace-frequency component matrices in the case 2 and the case 3 aresimilar to the specific method described in the case 1. For brevity,details are not described herein again.

Based on the foregoing technical solutions, the terminal device maygenerate the first indication information, to indicate the L₁ beamvectors in the beam vector set, the K₁ frequency domain vectors in thefrequency domain vector set, and the T₁ space-frequency componentmatrices.

It should be understood that foregoing methods for determining the L₁beam vectors in the beam vector set, the K₁ frequency domain vectors inthe frequency domain vector set, and the T₁ space-frequency componentmatrices are merely examples, and should not constitute any limitationon this application. As described above, the L₁ beam vectors may be someor all beam vectors in the beam vector set, that is, L₁≤L₀. The K₁frequency domain vectors may be some or all frequency domain vectors inthe frequency domain vector set, that is, K₁≤K₀. However, L₁, K₁, L₀,and K₀ do not satisfy L₁=L₀ and K₁=K₀ at the same time.

As described above, the L₁ beam vectors may be some or all beam vectorsin the beam vector set, that is, L₁≤L₀. The K₁ frequency domain vectorsmay be some or all frequency domain vectors in the frequency domainvector set, that is, K₁≤K₀. However, L₁, K₁, L₀, and K₀ do not satisfyL₁=L₀ and K₁=K₀ at the same time.

When the beam vector set or the frequency domain vector set isoversampled, the L₁ beam vectors may be a subset (for example, anorthogonal group) of the beam vector set or some beam vectors in asubset of the beam vector set, and the K₁ frequency domain vectors maybe a subset (for example, an orthogonal group) of the frequency domainvector set or some frequency domain vectors in a subset of the frequencydomain vector set. However, L₁, K₁, L₀, and K₀ do not satisfy L₁=L₀ andK₁=K₀ at the same time.

Optionally, when the L₁ beam vectors are a subset of the beam vector setand the first indication information is used to indicate the L₁ beamvectors, the first indication information may be used to indicate onlythe selected subset of the beam vector set, and the L₁ beam vectors arenot indicated by using additional information. When the network devicereceives the first indication information, it may be considered bydefault that the L₁ beam vectors are the selected subset of the beamvector set.

Optionally, when the K₁ frequency domain vectors are a subset of thefrequency domain vector set and the first indication information is usedto indicate the K₁ frequency domain vectors, the first indicationinformation may be used to indicate only the selected subset of thefrequency domain vector set, and the K₁ frequency domain vectors are notindicated by using additional information. When the network devicereceives the first indication information, it may be considered bydefault that the K₁ frequency domain vectors are the selected subset ofthe frequency domain vector set.

Optionally, when the L₁ beam vectors are a universal set of the beamvector set, that is, L₁=L₀, the first indication information mayindicate only the K₁ frequency domain vectors and the T₁ space-frequencyvector pairs, and does not indicate the L₁ beam vectors by usingadditional information. When the network device receives the firstindication information, it may be considered by default that the L₁ beamvectors are all beam vectors in the beam vector set. Optionally, whenthe K₁ frequency domain vectors are a universal set of the frequencydomain vector set, that is, K₁=K₀, the first indication information mayindicate only the L₁ beam vectors and the T₁ space-frequency vectorpairs, and does not indicate the K₁ frequency domain vectors by usingadditional information. When the network device receives the firstindication information, it may be considered by default that the K₁frequency domain vectors are all frequency domain vectors in thefrequency domain vector set.

It should be understood that the foregoing enumerated specific contentindicated by using the first indication information in different casesis merely an example, and should not constitute any limitation on thisapplication. For example, the terminal device may not distinguishbetween the foregoing listed cases, but directly indicate the L₁ beamvectors, the K₁ frequency domain vectors, and the T₁ space-frequencyvector pairs.

Implementation 2

The terminal device may determine the M₁ space-frequency componentmatrices based on a prestored space-frequency component matrix set and apredetermined space-frequency matrix, and further determine the T₁space-frequency component matrices.

In this embodiment, each space-frequency component matrix in thespace-frequency component matrix set prestored by the terminal devicemay be a matrix having a dimension of N_(s)×N_(f), or may be a vectorhaving a length of N_(s)×N_(f). With reference to the two cases, thefollowing separately describes in detail a specific process in which theterminal device determines the T₁ space-frequency component matrices.

Case A: Each space-frequency component matrix in the space-frequencycomponent matrix set is a vector having a length of N_(s)×N_(f).

It is assumed that precoding vectors of N_(f) frequency domain unitsdetermined by the terminal device are denoted as h₀, h₁, . . . , andh_(N) _(f) ⁻¹. In the case A, the terminal device may construct, basedon the precoding vectors of the N_(f) frequency domain units, aspace-frequency matrix H having a length of N_(s)×N_(f), where H

[h₀ ^(T) h₁ ^(T) . . . h_(N) _(f) ⁻¹ ^(T)]^(T). For ease ofdifferentiation, the space-frequency matrix whose length is N_(s)×N_(f)is referred to as a space-frequency vector below.

The following describes the space-frequency component matrix set indetail.

In a possible design, the space-frequency component matrix set mayinclude N_(S)×N_(f) space-frequency component matrices. Eachspace-frequency component matrix may be a vector having a length ofN_(S)×N_(f). For ease of differentiation and description below, thespace-frequency component matrix whose length is N_(S)×N_(f) is referredto as a space-frequency component vector. Correspondingly, thespace-frequency component matrix set may be referred to as aspace-frequency component vector set. A weighted sum of T₁space-frequency component vectors selected from the space-frequencycomponent vector set may be constructed to obtain a space-frequencyvector. The space-frequency vector obtained through construction byusing the weighted sum of the T₁ space-frequency component vectors maybe the same as or similar to the foregoing space-frequency vectordetermined by the terminal device.

In this embodiment of this application, each space-frequency componentvector in the space-frequency component vector set may be uniquelydetermined by one beam vector in the beam vector set and one frequencydomain vector in the frequency domain vector set. In other words, anytwo space-frequency component vectors in the space-frequency componentvector set are different, and any two space-frequency component vectorshave a difference in at least one of corresponding beam vectors andfrequency domain vectors.

Specifically, each space-frequency component vector in thespace-frequency component vector set may be a Kronecker product of onebeam vector in the beam vector set and one frequency domain vector inthe frequency domain vector set, or may be a Kronecker product of onefrequency domain vector in the frequency domain vector set and one beamvector in the beam vector set. To correspond to the space-frequencyvector constructed above, each space-frequency component vector in thespace-frequency component vector set may be uniquely determined by usinga Kronecker product of a frequency domain vector and a beam vector.

As described above, if an oversampling rate is not considered, the beamvector set may include N_(s) beam vectors, and the frequency domainvector set may include N_(f) frequency domain vectors. In this case, theN_(s)×N_(f) space-frequency component vectors may be determined based onthe beam vector set and the frequency domain vector set. That is, thespace-frequency component vector set may include N_(s)×N_(f)space-frequency component vectors. Each space-frequency component vectormay correspond to one beam vector and one frequency domain vector, oreach space-frequency component vector may correspond to aspace-frequency vector pair obtained by combining one beam vector andone frequency domain vector.

Each space-frequency component vector in the space-frequency componentvector set may correspond to one index. The N_(s)×N_(f) space-frequencycomponent vectors in the space-frequency component vector set may beindicated by using indexes in the space-frequency component vector set,or may be indicated by using indexes, in the beam vector set and thefrequency domain vector set respectively, of beam vectors and frequencydomain vectors that may be used to generate the space-frequencycomponent vectors. Indexes of the M₁ space-frequency component vectorsin the space-frequency component vector set may be considered asone-dimensional indexes of the M₁ space-frequency component vectors.Indexes, in the beam vector set and the frequency domain vector setrespectively, of beam vectors and frequency domain vectors included inthe M₁ space-frequency component vectors may be considered astwo-dimensional indexes of the M₁ space-frequency component vectors. Aone-dimensional index and a two-dimensional index may be mutuallyconverted according to a predefined conversion rule.

Specifically, it is assumed that m is an index of a space-frequencycomponent vector in the space-frequency component vector set,0≤m≤N_(s)×N_(f)−1, and m is an integer. n_(s) is an index of a beamvector in the beam vector set, 0≤n_(s)≤N_(s)−1, and n_(s) is an integer.n_(f) is an index of a frequency domain vector in the frequency domainvector set, 0≤n_(f)≤N_(f)−1 and n_(f) is an integer.

For example, N_(f) space-frequency component vectors determined by usingKronecker products of a 0^(th) beam vector in the N_(s) beam vectors anda 0^(th) frequency domain vector to an (N_(f)−1)^(th) frequency domainvector in the N_(f) frequency domain vectors may correspond toone-dimensional indexes 0 to N_(f)−1. N_(f) space-frequency componentvectors determined by using Kronecker products of the 1^(st) beam vectorin the N_(s) beam vectors and the 0^(th) frequency domain vector to the(N_(f)−1)^(th) frequency domain vector in the N_(f) frequency domainvectors may correspond to one-dimensional indexes N_(f) to 2N_(f)−1. Byanalogy, N_(f) space-frequency component vectors determined by usingKronecker products of an n_(s) ^(th) beam vector in the N_(s) beamvectors and the 0^(th) frequency domain vector to the (N_(f)−1)^(th)frequency domain vector in the N_(f) frequency domain vectors maycorrespond to one-dimensional indexes n_(s)×N_(f) to (n_(s)+1)×N_(f)−1.For ease of differentiation and description, the numbering rule may bedenoted as a rule 1.

Therefore, for the N_(s)×N_(f) space-frequency component vectors in thespace-frequency component vector set, it is assumed that an m^(th)space-frequency component vector may be indicated by using an n_(s)^(th) beam vector in the beam vector set and an n_(f) ^(th) frequencydomain vector in the frequency domain vector set. n_(f)=

m/N_(f)

, and n_(s)=mod(m, N_(f)).

represents rounding down, and mod( ) represents a modulo operation.

For the N_(s) beam vectors in the beam vector set and the N_(f)frequency domainvectors in the frequency domain vector set, aspace-frequency component vector constructed by using an n_(s) ^(th)beam vectors in the beam vector set and an n_(f) ^(th) frequency domainvector in the frequency domain vector set may be indicated by using anm^(th) space-frequency component vector, where m=n_(f)+n_(s)*N_(f). Foranother example, N_(s) space-frequency component vectors determined byusing Kronecker products of a₀th frequency domain vector in the N_(f)frequency domain vectors and a₀th beam vector to an (N_(s)−1)^(th) beamvector in the N_(s) beam vectors may correspond to one-dimensionalindexes 0 to N_(s)−1. N_(s) space-frequency component vectors determinedby using Kronecker products of a 1st frequency domain vector in theN_(f) frequency domain vectors and the 0^(th) beam vector to the(N_(s)−1)^(th) beam vector in the N_(s) beam vectors may correspond toone-dimensional indexes N_(s) to 2N_(s)−1. By analogy, N_(s)space-frequency component vectors determined by using Kronecker productsof an n_(f) ^(th) frequency domain vector in the N_(f) frequency domainvectors and the 0^(th) beam vector to the (N_(s)−1)^(th) beam vector inthe N_(s) beam vectors may correspond to one-dimensional indexesn_(f)×_(N)s to (n_(f)+1)×N_(s)−1. For ease of differentiation anddescription, the numbering rule may be denoted as a rule 2.

Therefore, for the N_(s)×N_(f) space-frequency component vectors in thespace-frequency component vector set, an m^(th) (0≤m≤N_(s)×N_(f)−1)space-frequency component vector may be indicated by using an n_(s)^(th) beam vector in the beam vector set and an n_(f) ^(th) frequencydomain vector in the frequency domain vector set. n_(s)=

m/N_(s)

, and n_(f)=mod(m, N_(s)).

For the N_(s) beam vectors in the beam vector set and the N_(s) beamvectors in the frequency domain vector set, a space-frequency componentvector constructed by using an n_(s) ^(th) beam vectors in the beamvector set and an n_(f) ^(th) frequency domain vector in the frequencydomain vector set may be indicated by using an m^(th) space-frequencycomponent vector, where m=n_(s)+n_(f)*N_(s).

It should be understood that the foregoing listed two manners ofnumbering the space-frequency component vectors in the space-frequencycomponent vector set are merely examples, and should not constitute anylimitation on this application. The terminal device and the networkdevice may number each space-frequency component vector in thespace-frequency component vector set according to a pre-agreed rule. Acorrespondence between each space-frequency component vector and anindex defined by the network device is consistent with a correspondencebetween each space-frequency component vector and an index defined bythe terminal device.

If the oversampling rate is considered, there may be the following threepossible cases for vectors included in the space-frequency componentvector set:

Case 1: The space-frequency component vector set is extended toO_(s)×N_(s)×O_(f)×N_(f) space-frequency component vectors by usingoversampling factors O_(s) and O_(f). In this case, the space-frequencycomponent vector set may include O_(s)×O_(f) subsets, and each subsetmay include N_(s)×N_(f) space-frequency component vectors.

Case 2: The space-frequency component vector set is extended toO_(s)×N_(s)×N_(f) space-frequency component vectors by using anoversampling factor O_(s). In this case, the space-frequency componentvector set may include O_(s) subsets, and each subset may includeN_(s)×N_(f) space-frequency component vectors.

Case 3: The space-frequency component vector set is extended toO_(f)×N_(s)×N_(f) space-frequency component vectors by using anoversampling factor O_(f). In this case, the space-frequency componentvector set may include O_(f) subsets, and each subset may includeN_(s)×N_(f) space-frequency component vectors.

In the foregoing three cases, the oversampling factor O_(s) may be anoversampling factor of the beam vector set, and the oversampling factorO_(f) may be an oversampling factor of the frequency domain vector set.If the oversampling factor of the space-frequency component vector setis denoted as O_(c), O_(c)=O_(s)×O_(f), O_(c)>1, and O_(c) is a positiveinteger. If the oversampling rate exists, O_(s) and O_(f) are not set to1 at the same time.

When the oversampling rate is considered, each subset of the beam vectorset and each subset of the frequency domain vector set may be separatelydetermined to obtain a plurality of groups of space-frequency componentvectors, and each group of space-frequency component vectors includeN_(s)×N_(f) space-frequency component vectors. A rule for numberingindexes of the N_(s)×N_(f) space-frequency component vectors in eachgroup of space-frequency component vectors may be the same as theforegoing numbering rule used when the oversampling rate is notconsidered. For brevity, details are not described herein again.

The following separately describes specific methods for determining andindicating, by the terminal device, the T₁ space-frequency componentvectors and the weighting coefficients of the space-frequency componentvectors when an oversampling rate is considered and when theoversampling rate is not considered.

If the oversampling rate is not considered, the terminal device maydetermine the T₁ space-frequency component vectors and the weightingcoefficients of the space-frequency component vectors by using step 3-ito step 3-iv shown below.

Step 3-i: The terminal device may determine a weighting coefficientmatrix based on the foregoing space-frequency vector and space-frequencycomponent vector set.

If the oversampling rate is not considered, the space-frequencycomponent vector set may include N_(s)×N_(f) space-frequency componentvectors. The terminal device may separately project the predeterminedspace-frequency vector to the N_(s)×N_(f) space-frequency componentvectors. That is, a conjugate transpose of each of the N_(s)×N_(f)space-frequency component vectors is multiplied by the space-frequencyvector, to obtain N_(s)×N_(f) projection values. An arrangement order ofthe N_(s)×N_(f) projection values is corresponding to an arrangementorder of the N_(s)×N_(f) space-frequency component vectors in thespace-frequency component vector set.

The terminal device may arrange the N_(s)×N_(f) projection values into amatrix whose dimension is N_(s)×N_(f) according to a pre-specifiedarrangement order and based on an arrangement order of the N_(s)×N_(f)space-frequency component vectors in the space-frequency componentvector set.

Specifically, if indexes of the N_(s)×N_(f) space-frequency componentvectors in the space-frequency component vector set are one-dimensionalindexes, and a rule for numbering the indexes of the N_(s)×N_(f)space-frequency component vectors is determined based on the foregoingrule 1, starting from a first projection value in the N_(s)×N_(f)projection values, the terminal device may use every N_(f) consecutiveprojection values as a row, to obtain N_(s) rows, where each rowincludes N_(f) projection values. The N_(s) rows are arranged in orderfrom top to bottom, and a matrix W whose dimension is N_(s)×N_(f) may beobtained.

If indexes of the N_(s)×N_(f) space-frequency component vectors in thespace-frequency component vector set are one-dimensional indexes, and arule for numbering the indexes of the N_(s)×N_(f) space-frequencycomponent vectors is determined based on the foregoing rule 2, startingfrom a first projection value in the N_(s)×N_(f) projection values, theterminal device may use every N_(s) consecutive projection values as acolumn, to obtain N_(f) columns, where each column includes N_(s)projection values. The N_(f) columns are arranged in order from left toright, and a matrix W whose dimension is N_(s)×N_(f) may be obtained.

If indexes of the N_(s)×N_(f) space-frequency component vectors in thespace-frequency component vector set are two-dimensional indexes, theterminal device may directly arrange the N_(s)×N_(f) space-frequencycomponent vectors into a matrix form based on the two-dimensionalindexes. For example, space-frequency component vectors that have a sameindex n_(s) are arranged in a same row, and space-frequency componentvectors that have a same index n_(f) are arranged in a same column.

The matrix W whose dimension is N_(s)×N_(f) may be referred to as aweighting coefficient matrix. N_(s)×N_(f) weighting coefficients in thematrix W may correspond to N_(s)×N_(f) space-frequency component vectorsin the space-frequency component vector set, and may represent aweighting coefficient of each of the N_(S)×N_(f) space-frequencycomponent vectors.

Step 3-ii: The terminal device may determine M₁ relatively strongspace-frequency component vectors based on the weighting coefficientmatrix.

The terminal device may separately perform modulo operations on theN_(s) rows in the matrix W, and determine L₁ rows with relatively largemoduli according to a modulus of each row. The L₁ rows with relativelylarge moduli are relatively strong L₁ rows. Further, the terminal devicemay separately perform modulo operations on the N_(f) columns in thematrix W, and determine K₁ columns with relatively large moduliaccording to a modulus of each column. The K₁ columns with relativelylarge moduli are relatively strong K₁ columns. The terminal device maydetermine the M₁ relatively strong space-frequency component vectors inthe space-frequency component vector set based on locations of the L₁relatively strong rows and the K₁ relatively strong columns in thematrix W and according to a predefined conversion rule.

Actually, each space-frequency component vector in the space-frequencycomponent vector set may be determined by using each beam vector in thebeam vector set and each frequency domain vector in the frequency domainvector set. The M₁ space-frequency component vectors may be determinedbased on the L₁ relatively strong beam vectors in the beam vector setand the K₁ relatively strong frequency domain vectors in the frequencydomain vector set. Row numbers of the foregoing determined L₁ relativelystrong rows in the matrix W may be sequence numbers of the L₁ relativelystrong beam vectors in the beam vector set, and column numbers of the K₁relatively strong columns in the matrix W may be sequence numbers of theK₁ relatively strong frequency domain vectors in the frequency domainvector set.

It should be understood that the foregoing described specific method fordetermining, by the terminal device, the L₁ relatively strong rows andthe K₁ relatively strong columns based on the weighting coefficientmatrix, to determine the M₁ relatively strong space-frequency componentvectors is merely an example for ease of understanding, and should notconstitute any limitation on this application. This application does notexclude a possibility that the terminal device determines the M₁relatively strong space-frequency component vectors in another manner.Provided that the M₁ relatively strong space-frequency component vectorsdetermined by the terminal device may be constructed by using the L₁beam vectors and the K₁ frequency domain vectors, all manners shouldfall within the protection scope of this application.

Step 3-iii: The terminal device may determine T₁ relatively strongspace-frequency component vectors in the M₁ relatively strongspace-frequency component vectors.

The terminal device may determine the T₁ relatively strongspace-frequency component vectors based on moduli of weightingcoefficients of the M₁ space-frequency component vectors. For example, amodulus of a weighting coefficient of any one of the selected T₁space-frequency component vectors is greater than or equal to a modulusof any one of remaining M₁-T₁ space-frequency component vectors. Inaddition, weighting coefficients of the T₁ space-frequency componentvectors can also be determined.

Step 3-iv: The terminal device generates the first indicationinformation, to indicate the L₁ beam vectors, the K₁ frequency domainvectors, and the T₁ space-frequency component vectors.

Based on the M₁ space-frequency component vectors and the T₁space-frequency component vectors that are determined in the foregoingstep 3-i to step 3-iii, the first indication information may includelocation information of the M₁ space-frequency component vectors in thespace-frequency component vector set or a subset of the space-frequencycomponent vector set, and information used to indicate the T₁space-frequency component vectors.

Optionally, when the first indication information is used to indicatethe M₁ space-frequency component vectors, the first indicationinformation may be specifically used to indicate two-dimensional indexesof the M₁ space-frequency component vectors, that is, indexes, in thebeam vector set, of the L₁ beam vectors included in the M₁space-frequency component vectors and indexes, in the frequency domainvector set, of the K₁ frequency domain vectors included in the M₁space-frequency component vectors.

The specific method for indicating the L₁ beam vectors and the K₁frequency domain vectors by using the first indication information, andbit overheads have been described in detail in the foregoingImplementation 1. For brevity, details are not described herein again.

Optionally, when the first indication information is used to indicatethe M₁ space-frequency component vectors, the first indicationinformation may be specifically used to indicate indexes of the M₁space-frequency component vectors in the space-frequency componentvector set or a subset of the space-frequency component vector set. Asdescribed above, a rule for numbering indexes of a plurality ofspace-frequency component vectors may be predefined in a protocol, andthe terminal device and the network device may determine an index ofeach space-frequency component vector in the space-frequency componentvector set based on the same numbering rule. That is, locationinformation of the M₁ space-frequency component vectors may be an indexof each space-frequency component vector in the space-frequencycomponent vector set. In this case, the terminal device may indicateeach of the M₁ space-frequency component vectors by using log₂

N_(s)×N_(f)

bits.

Optionally, when the first indication information is used to indicatethe M₁ space-frequency component vectors, the first indicationinformation may be specifically used to indicate an index of acombination of the M₁ space-frequency component vectors in thespace-frequency component vector set. For example, a plurality ofcombinations of a plurality of space-frequency component vectors may bepredefined in a protocol, and each combination corresponds to one index.The M₁ space-frequency component vectors may be one of the plurality ofcombinations, or may be close to one of the plurality of combinations.The first indication information may indicate the M₁ space-frequencycomponent vectors by indicating an index of the combination. That is,location information of the M₁ space-frequency component vectors may bethe index of the combination of the M₁ space-frequency component vectorsin the space-frequency component vector set. In this case, the terminaldevice may indicate the M₁ space-frequency component vectors in thespace-frequency component vector set by using log₂

C_(N) _(s) _(×n) _(f) ^(M) ¹

bits.

It should be noted that, because each space-frequency component vectorin the space-frequency component vector set is uniquely determined byusing one beam vector and one frequency domain vector, that the firstindication information is used to indicate the locations of the M₁space-frequency component vector in the space-frequency component vectorset may also be understood as that the first indication information isused to indirectly indicate locations, in the beam vector set and in thefrequency domain vector set respectively, of a beam vector and afrequency domain vector that correspond to each space-frequencycomponent vector. In other words, the location information of the M₁space-frequency component vectors may be mutually converted into thelocation information of the L₁ beam vectors and the location informationof the K₁ frequency domain vectors, or vice versa. Alternatively, thelocation information of the M₁ space-frequency component vectors may beequivalent to the location information of the L₁ beam vectors and thelocation information of the K₁ frequency domain vectors. In other words,when the first indication information is used to indicate the M₁space-frequency component vectors, the first indication information isused to indirectly indicate the L₁ beam vectors and the K₁ frequencydomain vectors.

It should be understood that the foregoing enumerated two methods forindicating the M₁ space-frequency component vectors are merely examples,and should not constitute any limitation on this application.Alternatively, the first indication information may indicate the M₁space-frequency component vectors in another manner.

Optionally, the first indication information may be used to indicate theT₁ space-frequency component vectors in any one of the followingmanners:

Manner 1: The T₁ space-frequency component vectors in the M₁space-frequency component vectors are indicated by using a bitmap(bitmap).

Manner 2: An index of a combination of the T₁ space-frequency componentvectors in the M₁ space-frequency component vectors is indicated.

Manner 3: Locations, in the L₁ beam vectors, of beam vectorscorresponding to the T₁ space-frequency component vectors and locations,in the K₁ frequency domain vectors, of frequency domain vectorscorresponding to the T₁ space-frequency component vectors are indicated.

Manner 4: A location, in the M₁ space-frequency vector pairs, of each ofthe T₁ space-frequency vector pairs is indicated.

The specific process of indicating the T₁ space-frequency vector pairsbased on the manner 1, the manner 2, the manner 3, and the manner 4, andbit overheads separately caused by the manner 1, the manner 2, themanner 3, and the manner 4 have been described in detail above. Forbrevity, details are not described herein again.

Optionally, the first indication information further includesquantization information of the weighting coefficients of the T₁space-frequency vector pairs.

The specific process in which the first indication information is usedto indicate the weighting coefficients of the T₁ space-frequencycomponent vectors has been described in detail in the foregoingImplementation 1. A specific manner that is in Implementation 2 and inwhich the first indication information is used to indicate the weightingcoefficients of the T₁ space-frequency component vectors may be the sameas the specific manner provided in Implementation 1. For brevity,details are not described herein again.

It should be understood that the quantization information of theweighting coefficients of the T₁ space-frequency vector pairs may becarried in the first indication information, or may be carried inadditional information. This is not limited in this application.

If the oversampling rate is considered, the terminal device mayspecifically determine the T₁ space-frequency component vectors and theweighting coefficients of the space-frequency component vectors by usingstep 4-i to step 4-iv shown below.

Step 4-i: The terminal device may determine a plurality of weightingcoefficient matrices based on the space-frequency vectors and eachsubset in the space-frequency component vector set.

If the space-frequency component vector set is extended toO_(c)×N_(S)×N_(f) space-frequency component vectors by using anoversampling factor O_(c), the space-frequency component vector set mayinclude O_(c) subsets. The terminal device may separately project thepredetermined space-frequency vector to N_(S)×N_(f) space-frequencycomponent vectors in each subset, to obtain O_(c) groups of projectionvalues, where each group of projection values includes N_(S)×N_(f)projection values. For each group of projection values, an arrangementorder of the N_(S)×N_(f) projection values corresponds to an arrangementorder of the N_(S)×N_(f) space-frequency component vectors in eachsubset of the space-frequency component vector set.

The terminal device may arrange the N_(s)×N_(f) projection values into amatrix whose dimension is N_(S)×N_(f) according to a pre-specifiedarrangement order and based on an arrangement order of the N_(S)×N_(f)space-frequency component vectors in each subset. Therefore, O_(c)matrices corresponding to the O_(c) subsets may be obtained, each matrixmay correspond to one subset, and each matrix may be referred to as aweighting coefficient matrix corresponding to the subset. The foregoinghas described in detail a specific method for constructing a matrix withreference to a rule for numbering indexes of space-frequency componentvectors in a space-frequency component vector set. For brevity, detailsare not described herein again.

The O_(c) weighting coefficient matrices corresponding to the O_(c)subsets may be denoted as o_(c)=0, 1, . . . , and O_(c)−1. In the matrixW₀, N_(S)×N_(f) weighting coefficients may correspond to N_(s)×N_(f)space-frequency component vectors in an o_(c) ^(th) subset in thespace-frequency component vector set, and may represent weightingcoefficients of all space-frequency component vectors in the subset.

Step 4-ii: The terminal device may determine O_(c) groups ofspace-frequency component vectors based on the O_(c) subsets in thespace-frequency component set, where each group of space-frequencycomponent vectors may include T₁ space-frequency component vectors.

The terminal device may traverse 0 to O_(c)−1 for a value of o_(c), andrepeatedly perform the following steps, to determine the O_(c) group ofspace-frequency component vectors: determining L₁ relatively strong rowsand K₁ relatively strong columns based on the matrix W_(o) _(c) , todetermine M₁ relatively strong space-frequency component vectors in theo_(c) ^(th) subset. The terminal device may further determine T₁relatively strong space-frequency component vectors in the M₁space-frequency component vectors.

The foregoing specific processes in which the terminal device determinesthe M₁ relatively strong space-frequency component vectors based on theweighting coefficient matrix and determines the T₁ relatively strongspace-frequency component vectors in the M₁ space-frequency componentvectors have been described in detail in step 3-ii and step 3-iii. Forbrevity, details are not described herein again.

Step 4-iii: The terminal device may select a strongest group ofspace-frequency component vectors based on weighting coefficient of theO_(c) groups of space-frequency component vectors, to determine the T₁space-frequency component vectors.

The terminal device may determine the strongest group of space-frequencycomponent vectors based on the O_(c) group space-frequency componentvectors determined in step 4-ii. For example, the terminal device maycalculate a sum of moduli of weighting coefficients of each group ofspace-frequency component vectors in the O_(c) groups of space-frequencycomponent vectors, and determine a group of space-frequency componentvectors whose sum of moduli is the largest as the strongest group ofspace-frequency component vectors. Therefore, the T₁ space-frequencycomponent vectors and the weighting coefficients of the space-frequencycomponent vectors can be determined.

Because the T₁ space-frequency component vectors are from a same subset,when determining the T₁ space-frequency component vectors, the terminaldevice can also determine a subset to which the T₁ space-frequencycomponent vectors belong. In this way, the M₁ relatively strongspace-frequency component vectors in the subset can be determined.

Step 4-iv: The terminal device generates the first indicationinformation, to indicate the L₁ beam vectors, the K₁ frequency domainvectors, and the T₁ space-frequency component vectors.

Based on the M₁ space-frequency component vectors and the T₁space-frequency component vectors that are determined in the foregoingstep 4-i to step 4-iii, the first indication information may includelocation information of the M₁ space-frequency component vectors in thespace-frequency component vector set or a subset of the space-frequencycomponent vector set, and information used to indicate the T₁space-frequency vectors component.

Optionally, when the first indication information is used to indicatethe M₁ space-frequency component vectors, the first indicationinformation may be specifically used to indicate location information,in the beam vector set, of L₁ beam vectors included in the M₁space-frequency component vectors and location information, in thefrequency domain vector set, of K₁ frequency domain vectors included inthe M₁ space-frequency component vectors, may be specifically used toindicate a subset to which the M₁ space-frequency component vectorsbelong and indexes of the M₁ space-frequency component vectors in thesubset, or may be specifically used to indicate a subset to which the M₁space-frequency component vectors belong and an index of a combinationof the M₁ space-frequency component vectors in the subset.

The location information of the L₁ beam vectors in the beam vector setmay be indexes of the L₁ beam vectors in the beam vector set, an indexof a combination of the L₁ beam vectors in the beam vector set, an indexof a subset to which the L₁ beam vectors belong and indexes of the L₁beam vectors in the subset, or an index of a subset to which the L₁ beamvectors belong and an index of a combination of the L₁ beam vectors inthe subset.

The location information of the K₁ frequency domain vectors in thefrequency domain vector set may be an index of the K₁ frequency domainvectors in the frequency domain vector set, an index of a combination ofthe K₁ frequency domain vectors in the frequency domain vector set, anindex of a subset to which the K₁ frequency domain vectors belong andindexes of the K₁ frequency domain vectors in the subset, or an index ofa subset to which the K₁ frequency domain vectors belong and an index ofa combination of the K₁ frequency domain vectors in the subset.

It should be noted that, because each space-frequency component vectorin the space-frequency component vector set is uniquely determined byusing one beam vector and one frequency domain vector, that the firstindication information is used to indicate the locations of the M₁space-frequency component vector in the space-frequency component vectorset may also be understood as that the first indication information isused to indirectly indicate locations, in the beam vector set and in thefrequency domain vector set respectively, of a beam vector and afrequency domain vector that correspond to each space-frequencycomponent vector. In other words, the location information of the M₁space-frequency component vectors may be mutually converted into thelocation information of the L₁ beam vectors and the location informationof the K₁ frequency domain vectors, or vice versa. Alternatively, thelocation information of the M₁ space-frequency component vectors may beequivalent to the location information of the L₁ beam vectors and thelocation information of the K₁ frequency domain vectors. In other words,when the first indication information is used to indicate the M₁space-frequency component vectors, the first indication information isused to indirectly indicate the L₁ beam vectors and the K₁ frequencydomain vectors.

When the first indication information is used to indicate the T₁space-frequency component vectors, a specific indication manner may beany one of the manner 1 to the manner 4 described above. The specificprocess of indicating the T₁ space-frequency component vectors based onthe manner 1, the manner 2, the manner 3, and the manner 4 separately,and bit overheads separately caused by the manner 1, the manner 2, themanner 3, and the manner 4 have been described in detail above. Forbrevity, details are not described herein again.

Optionally, the first indication information further includesquantization information of the weighting coefficients of the T₁space-frequency component vectors.

The specific process in which the first indication information is usedto indicate the weighting coefficients of the T₁ space-frequencycomponent vectors has been described in detail in the foregoingImplementation 1. A specific manner that is in Implementation 2 and inwhich the first indication information is used to indicate the weightingcoefficients of the T₁ space-frequency component vectors may be the sameas the specific manner provided in Implementation 1. For brevity,details are not described herein again.

It should be understood that the quantization information of theweighting coefficients of the T₁ space-frequency component vectors maybe carried in the first indication information, or may be carried inadditional information. This is not limited in this application.

Case B: Each space-frequency component matrix in the space-frequencycomponent matrix set is a matrix having a dimension of N_(s)×N_(f).

It is assumed that precoding vectors of N_(f) frequency domain unitsdetermined by the terminal device are denoted as h₀, h₁, . . . , andh_(N) _(f) ⁻¹. In the case B, the terminal device may construct, basedon the precoding vectors of the N_(f) frequency domain units, aspace-frequency

matrix H having a dimension of N_(S)×N_(f), where H

[h₀ h₁ . . . h_(N) _(f) ⁻¹].

The following describes the space-frequency component matrix set indetail.

In a possible design, the space-frequency component matrix set mayinclude N_(S)×N_(f) space-frequency component matrices. Eachspace-frequency component matrix may be a matrix having a dimension ofN_(s)×N_(f). A weighted sum of T₁ space-frequency component matricesselected from the space-frequency component matrix set may be used toconstruct a space-frequency matrix. The space-frequency matrix obtainedthrough construction by using the weighted sum of the T₁ space-frequencycomponent matrices may be the same as or similar to the foregoingspace-frequency matrix determined by the terminal device.

In this embodiment of this application, each space-frequency componentmatrix in the space-frequency component matrix set may be uniquelydetermined by one beam matrix in the beam matrix set and one frequencydomain matrix in the frequency domain matrix set. In other words, anytwo space-frequency component matrices in the space-frequency componentmatrix set are different, and any two space-frequency component matriceshave a difference in at least one of corresponding beam matrices andfrequency domain matrices. Specifically, each space-frequency componentmatrix in the space-frequency component matrix set may be a product of abeam vector in the beam vector set and a conjugate transpose of afrequency domain vector in the frequency domain vector set.

As described above, if the oversampling rate is not considered, thespace-frequency component matrix set may include N_(s)×N_(f)space-frequency component matrices. Each space-frequency componentmatrix may correspond to one beam vector and one frequency domainvector, or each space-frequency component matrix may correspond to aspace-frequency vector pair obtained by combining one beam vector andone frequency domain vector.

Each space-frequency component matrix in the space-frequency componentmatrix set may correspond to one one-dimensional index, or maycorrespond to one two-dimensional index. That is, the N_(S)×N_(f)space-frequency component matrices in the space-frequency componentmatrix set may be indicated by using indexes in the space-frequencycomponent matrix set or the subsets of the space-frequency componentmatrix set, or may be indicated by using indexes, in the beam vector setand the frequency domain vector set respectively, of a beam vector and afrequency domain vector that may be used to generate a space-frequencycomponent matrix. In the foregoing case A, a correspondence between eachspace-frequency component matrix and a one-dimensional index and a rulefor conversion between a one-dimensional index and a two-dimensionalindex have been described in detail with reference to the numbering rule1 and the numbering rule 2. For brevity, details are not describedherein again.

If the oversampling rate is considered, the space-frequency componentmatrix set may be extended to O_(c)×N_(S)×N_(f) space-frequencycomponent matrices by using an oversampling factor O_(c). Thespace-frequency component matrix set may include O_(c) subsets, and eachsubset may include N_(S)×N_(f) space-frequency component matrices. Arule for numbering an index of a space-frequency component matrix ineach subset may be the same as the numbering rule used when theoversampling rate is not considered. For brevity, details are notdescribed herein again.

The following separately describes specific methods for determining andindicating, by the terminal device, the T₁ space-frequency componentmatrices and the weighting coefficients of the space-frequency componentmatrices when an oversampling rate is considered and when theoversampling rate is not considered.

If the oversampling rate is not considered, the terminal device maydetermine the T₁ space-frequency component matrices and the weightingcoefficients of the space-frequency component matrices by using step 5-ito step 5-iv shown below.

Step 5-i: The terminal device may determine a weighting coefficientbased on the space-frequency matrix and the space-frequency componentmatrix set.

If the oversampling rate is not considered, the space-frequencycomponent matrix set may include N_(s)×N_(f) space-frequency componentmatrices, and a dimension of each space-frequency component matrix maybe N_(s)×N_(f). The terminal device may determine N_(s)×N_(f) weightingcoefficients based on the predetermined space-frequency matrix and theN_(S)×N_(f) space-frequency component matrices.

Specifically, the terminal device may separately sum a product of aconjugate of each element in each space-frequency component matrix and acorresponding element in the space-frequency matrix, to obtainN_(s)×N_(f) values corresponding to the N_(s)×N_(f) space-frequencycomponent matrices. For example, an element in one space-frequencycomponent matrix in the space-frequency component matrix set is denotedas a_(p,q) (p=0, 1, . . . , N_(s)−1, and q=0, 1, . . . , N_(f)−1), andan element in the space-frequency matrix is denoted as b_(p,q).Therefore, a sum of products of conjugates of elements in eachspace-frequency component matrix and corresponding elements in thespace-frequency matrix may be represented as

$\sum\limits_{q = 0}^{N_{f} - 1}{\sum\limits_{p = 0}^{N_{s} - 1}{{\overset{\_}{a}}_{p,q}{b_{p,q}.}}}$

represents a conjugate of an element a_(p,q). This step is repeatedlyperformed on N_(s)×N_(f) space-frequency component matrices in thespace-frequency component matrix set, to obtain the N_(s)×N_(f) values.The N_(S)×N_(f) values may be considered as the N_(S)×N_(f) weightingcoefficients.

The foregoing step may be implemented by performing a matrix operation.For example, the N_(S)×N_(f) values may be obtained by calculating atrace of a product of a conjugate transpose of each space-frequencycomponent matrix and the space-frequency matrix.

Then, the terminal device may arrange the N_(s)×N_(f) values into amatrix whose dimension is N_(s)×N_(f) according to a pre-specifiedarrangement order and based on an arrangement order of the N_(s)×N_(f)space-frequency component matrices in the space-frequency componentmatrix set. A specific process in which the terminal device arranges theN_(s)×N_(f) values into the matrix whose dimension is N_(s)×N_(f)according to the pre-specified order has been described in detail in theforegoing case A. For brevity, details are not described herein again.

The matrix W whose dimension is N_(s)×N_(f) may be referred to as aweighting coefficient matrix. N_(s)×N_(f) weighting coefficients in thematrix W may correspond to N_(s)×N_(f) space-frequency componentmatrices in the space-frequency component matrix set, and may representa weighting coefficient of each of the N_(s)×N_(f) space-frequencycomponent matrices.

Step 5-ii: The terminal device may determine M₁ relatively strongspace-frequency component matrices based on the weighting coefficientmatrix.

A specific method used by the terminal device to determine the M₁space-frequency component matrices based on the weighting coefficientmatrix is the same as the specific method used by the terminal device todetermine the M₁ relatively strong space-frequency component vectorsbased on the weighting coefficient matrix in step 3-ii in the foregoingcase A. Because the specific method has described in detail above, forbrevity, details are not described herein again.

Step 5-iii: The terminal device may determine T₁ relatively strongspace-frequency component matrices in the M₁ space-frequency componentmatrices.

The terminal device may determine the T₁ relatively strongspace-frequency component matrices based on moduli of weightingcoefficients of the M₁ space-frequency component matrices. For example,a modulus of a weighting coefficient of any one of the selected T₁space-frequency component matrices is greater than or equal to a modulusof any one of remaining M₁-T₁ space-frequency component matrices. Inaddition, weighting coefficients of the T₁ space-frequency componentmatrices can also be determined.

Step 5-iv: The terminal device generates the first indicationinformation, to indicate the L₁ beam vectors, the K₁ frequency domainvectors, and the T₁ space-frequency component matrices.

Based on the M₁ space-frequency component matrices and the T₁space-frequency component matrices that are determined in the foregoingstep 5-i to step 5-iii, the first indication information may includelocation information of the M₁ space-frequency component matrices in thespace-frequency component matrix set or a subset of the space-frequencycomponent matrix set, and information used to indicate the T₁space-frequency component matrices.

Optionally, the first indication information further includesquantization information of the weighting coefficients of the T₁space-frequency component matrices.

In the foregoing case A, the specific method for indicating the M₁space-frequency component matrices, the T₁ space-frequency componentmatrices, and the weighting coefficients of the space-frequencycomponent matrices by using the first indication information, and bitoverheads have been described in detail. Bit overheads and a specificmethod for indicating the M₁ space-frequency component matrices, the T₁space-frequency component matrices, and the weighting coefficients ofthe space-frequency component matrices by using the first indicationinformation in the case B are the same as the method shown in the caseA. For brevity, details are not described herein again.

It should be noted that, because each space-frequency component matrixin the space-frequency component matrix set is uniquely determined byusing one beam vector and one frequency domain vector, that the firstindication information is used to indicate the locations of the M₁space-frequency component matrix in the space-frequency component matrixset may also be understood as that the first indication information isused to indirectly indicate locations, in the beam vector set and in thefrequency domain vector set respectively, of a beam vector and afrequency domain vector that correspond to each space-frequencycomponent matrix. In other words, the location information of the M₁space-frequency component matrices may be mutually converted into thelocation information of the L₁ beam vectors and the location informationof the K₁ frequency domain vectors, or vice versa. Alternatively, thelocation information of the M₁ space-frequency component matrices may beequivalent to the location information of the L₁ beam vectors and thelocation information of the K₁ frequency domain vectors. In other words,when the first indication information is used to indicate the M₁space-frequency component matrices, the first indication information isused to indirectly indicate the L₁ beam vectors and the K₁ frequencydomain vectors.

It should be understood that the quantization information of theweighting coefficients of the T₁ space-frequency component matrices maybe carried in the first indication information, or may be carried inadditional information. This is not limited in this application.

If the oversampling rate is considered, the terminal device mayspecifically determine the T₁ space-frequency component matrices and theweighting coefficients of the space-frequency component matrices byusing step 6-i to step 6-iv shown below.

Step 6-i: The terminal device may determine a plurality of weightingcoefficient matrices based on the space-frequency vectors and eachsubset in the space-frequency component matrix set.

If the space-frequency component matrix set is extended toO_(c)×N_(S)×N_(f) space-frequency component matrices by using anoversampling factor O_(c), the space-frequency component matrix set mayinclude O_(c) subsets. The terminal device may determine O_(c) groups ofweighting coefficients based on the predetermined space-frequency matrixand the O_(c) subsets, and each group of weighting coefficients includesN_(s)×N_(f) weighting coefficients. For a specific method fordetermining each group of weighting coefficients by the terminal device,refer to the foregoing implementation in step 5-i. For brevity, detailsare not described herein again. For each group of weightingcoefficients, an arrangement order of the N_(s)×N_(f) values correspondsto an arrangement order of the N_(S)×N_(f) space-frequency componentmatrices in each subset of the space-frequency component matrix set.

The terminal device may arrange the N_(s)×N_(f) weighting coefficientsinto a matrix whose dimension is N_(S)×N_(f) according to apre-specified arrangement order and based on an arrangement order of theN_(s)×N_(f) space-frequency component matrices in each subset.Therefore, O_(c) matrices corresponding to the O_(c) subsets may beobtained, each matrix may correspond to one subset, and each matrix maybe referred to as a weighting coefficient matrix corresponding to thesubset. The foregoing has described in detail a specific method forconstructing a matrix with reference to a rule for numbering indexes ofspace-frequency component matrices in a space-frequency component matrixset. For brevity, details are not described herein again.

The O_(c) weighting coefficient matrices corresponding to the O_(c)subsets may be denoted as o_(c)=0, 1, . . . , and O_(c)−1. In the matrixW₀, N_(S)×N_(f) weighting coefficients may correspond to N_(s)×N_(f)space-frequency component matrices in an o_(c) ^(th) subset in thespace-frequency component matrix set, and may represent weightingcoefficients of all space-frequency component matrices in the subset.

Step 6-ii: The terminal device may determine O_(c) groups ofspace-frequency component matrices based on the O_(c) subsets in thespace-frequency component set, where each group of space-frequencycomponent matrices may include T₁ space-frequency component matrices.

The terminal device may traverse 0 to O_(c)−1 for a value of o_(c), andrepeatedly perform the following steps, to determine the O_(c) group ofspace-frequency component matrices: determining L₁ relatively strongrows and K₁ relatively strong columns based on the matrix W_(o) _(c) ,to determine M₁ relatively strong space-frequency component matrices inthe o_(c) ^(th) subset. The terminal device may further determine T₁relatively strong space-frequency component matrices in the M₁space-frequency component matrices.

The foregoing specific processes in which the terminal device determinesthe M₁ relatively strong space-frequency component matrices based on theweighting coefficient matrix and determines the T₁ relatively strongspace-frequency component matrices in the M₁ space-frequency componentmatrices have been described in detail in step 3-ii and step 3-iii. Forbrevity, details are not described herein again.

Step 6-iii: The terminal device may select a strongest group ofspace-frequency component matrices based on weighting coefficient of theO_(c) groups of space-frequency component matrices, to determine the T₁space-frequency component matrices.

The terminal device may determine the strongest group of space-frequencycomponent matrices based on the O_(c) group space-frequency componentmatrices determined in step 6-ii. For example, the terminal device maycalculate a sum of moduli of weighting coefficients of each group ofspace-frequency component matrices in the O_(c) groups ofspace-frequency component matrices, and determine a group ofspace-frequency component matrices whose sum of moduli is the largest asthe strongest group of space-frequency component matrices. Therefore,the T₁ space-frequency component matrices and the weighting coefficientsof the space-frequency component matrices can be determined.

Because the T₁ space-frequency component matrices are from a samesubset, when determining the T₁ space-frequency component matrices, theterminal device can also determine a subset to which the T₁space-frequency component matrices belong. In this way, the M₁relatively strong space-frequency component matrices in the subset canbe determined.

Step 6-iv: The terminal device generates the first indicationinformation, to indicate the L₁ beam vectors, the K₁ frequency domainvectors, and the T₁ space-frequency component matrices.

Based on the M₁ space-frequency component matrices and the T₁space-frequency component matrices that are determined in the foregoingstep 6-i to step 6-iii, the first indication information may includelocation information of the M₁ space-frequency component matrices in thespace-frequency component matrix set or a subset of the space-frequencycomponent matrix set, and information used to indicate the T₁space-frequency component matrices.

Optionally, the first indication information further includesquantization information of the weighting coefficients of the T₁space-frequency component matrices.

In the foregoing case A, the specific method for indicating the M₁space-frequency component matrices, the T₁ space-frequency componentmatrices, and the weighting coefficients of the space-frequencycomponent matrices by using the first indication information, and bitoverheads have been described in detail. Bit overheads and a specificmethod for indicating the M₁ space-frequency component matrices, the T₁space-frequency component matrices, and the weighting coefficients ofthe space-frequency component matrices by using the first indicationinformation in the case B are the same as the method shown in the caseA. For brevity, details are not described herein again.

It should be noted that, because each space-frequency component matrixin the space-frequency component matrix set is uniquely determined byusing one beam vector and one frequency domain vector, that the firstindication information is used to indicate the locations of the M₁space-frequency component matrix in the space-frequency component matrixset may also be understood as that the first indication information isused to indirectly indicate locations, in the beam vector set and in thefrequency domain vector set respectively, of a beam vector and afrequency domain vector that correspond to each space-frequencycomponent matrix. In other words, the location information of the M₁space-frequency component matrices may be mutually converted into thelocation information of the L₁ beam vectors and the location informationof the K₁ frequency domain vectors, or vice versa. Alternatively, thelocation information of the M₁ space-frequency component matrices may beequivalent to the location information of the L₁ beam vectors and thelocation information of the K₁ frequency domain vectors. In other words,when the first indication information is used to indicate the M₁space-frequency component matrices, the first indication information isused to indirectly indicate the L₁ beam vectors and the K₁ frequencydomain vectors.

It should be understood that the quantization information of theweighting coefficients of the T₁ space-frequency component matrices maybe carried in the first indication information, or may be carried inadditional information. This is not limited in this application.

It should be further understood that the foregoing method fordetermining the L₁ relatively strong rows and the K₁ relatively strongcolumns by using the weighting coefficient matrix is merely a possibleimplementation shown for ease of understanding, but this does notindicate that the terminal device definitely generates the weightingcoefficient matrix when determining the L₁ relatively strong rows andthe K₁ relatively strong columns. For example, the terminal device maydetermine a plurality of weighting coefficients based on a precodingvector of each frequency domain unit and each space-frequency componentmatrix in the space-frequency component matrix set. The plurality ofweighting coefficients may form an array set, and elements in the arrayset may be obtained by sequentially connecting elements in rows (orcolumns) in the foregoing weighting coefficient matrix.

For another example, for a method for obtaining the beam vector by theterminal device, refer to a type II codebook feedback manner defined inan NR protocol. A frequency domain vector is obtained by comparing atleast one composition element (for example, but not limited to, aweighting coefficient that is of a beam vector and that constitutes aprecoding vector) of the precoding vector of each frequency domain unitat a same transport layer in a same polarization direction, to obtain achange rule in frequency domain. A same group of frequency domainvectors may be used in different polarization directions.

It should be further understood that the foregoing enumerated specificmethod used by the terminal device to determine the T₁ relatively strongspace-frequency component matrices in the M₁ space-frequency componentmatrices is merely an example, and should not constitute any limitationon this application. The terminal device may determine the T₁ relativelystrong space-frequency component matrices in the M₁ space-frequencycomponent matrices by referring to a method in the current technology.For brevity, details are not described herein.

It should be further understood that the foregoing listed specificmethod for determining and indicating the weighting coefficients of theT₁ space-frequency vector pairs (or the T₁ space-frequency componentvectors, or the T₁ space-frequency component matrices) and the foregoinglisted signaling are merely examples. Specific signaling and a specificmethod for determining and indicating the weighting coefficients of theT₁ space-frequency vector pairs (or the T₁ space-frequency componentvectors, or the T₁ space-frequency component matrices) are not limitedin this application, and may be the same as those in the currenttechnology.

It should be noted that, because each space-frequency component matrixin the space-frequency component matrix set is uniquely determined byusing one beam vector and one frequency domain vector, that the firstindication information is used to indicate the locations of the M₁space-frequency component matrix in the space-frequency component matrixset may also be understood as that the first indication information isused to indirectly indicate locations, in the beam vector set and in thefrequency domain vector set respectively, of a beam vector and afrequency domain vector that correspond to each space-frequencycomponent matrix. In other words, the location information of the M₁space-frequency component matrices may be mutually converted into thelocation information of the L₁ beam vectors and the location informationof the K₁ frequency domain vectors, or vice versa.

Based on the foregoing enumerated implementations of the terminal devicein different cases, the terminal device may generate the firstindication information, to indicate the L₁ beam vectors, the K₁frequency domain vectors, and the T₁ space-frequency component matricesthat are selected, and the weighting coefficients of the space-frequencycomponent matrices.

In step 220, the terminal device sends the first indication information.Correspondingly, in step 220, the network device receives the firstindication information.

Specifically, the first indication information may be a PMI, may be someinformation elements in a PMI, or may be other information. This is notlimited in this application. The first indication information may becarried in one or more messages in the current technology and sent bythe terminal device to the network device, or may be carried in one ormore messages newly designed in this application and sent by theterminal device to the network device. For example, the terminal devicemay send the first indication information to the network device by usinga physical uplink resource such as a physical uplink shared channel(physical uplink share channel, PUSCH) or a physical uplink controlchannel (physical uplink control channel, PUCCH), so that the networkdevice restores the precoding vector based on the first indicationinformation.

A specific method used by the terminal device to send the firstindication information to the network device by using the physicaluplink resource may be the same as that in the current technology. Forbrevity, detailed descriptions of a specific sending process are omittedherein.

In step 230, the network device determines a precoding vector of one ormore frequency domain units based on the first indication information.

It has been described in step 210 that the terminal device may generatethe first indication information based on two different implementations.In the implementations, in the first indication information, informationused to indicate the L₁ beam vectors and information used to indicatethe K₁ frequency domain vectors may be different, or may be the same.The following describes in detail a specific process in which thenetwork device determines the precoding vector of the one or morefrequency domain units based on the first indication information.

Optionally, the first indication information includes the locationinformation of the L₁ beam vectors, the location information of the K₁frequency domain vectors, and the information used to indicate the T₁space-frequency component matrices.

First, the network device may determine the selected L₁ beam vectors andthe selected K₁ frequency domain vectors based on the locationinformation of the L₁ beam vectors and the location information of theK₁ frequency domain vectors.

For example, the network device may determine the selected L₁ beamvectors in the beam vector set based on the index, indicated by usingthe first indication information, of the combination of the L₁ beamvectors in the beam vector set, and a predefined correspondence betweena beam vector combination and an index. Further, the network device maydetermine the selected K₁ frequency domain vectors in the frequencydomain vector set based on the index, indicated by using the firstindication information, of the combination of the K₁ frequency domainvectors in the frequency domain vector set, and a predefinedcorrespondence between a frequency domain vector combination and anindex. The L₁ beam vectors and the K₁ frequency domain vectors may becombined to obtain M₁ space-frequency vector pairs.

Then, the network device may determine the T₁ space-frequency componentmatrices in the M₁ space-frequency vector pairs based on the informationused to indicate the T₁ space-frequency component matrices.

As described above, the first indication information may be used toindicate the T₁ space-frequency vector pairs to the network device indifferent manners. For example, in the manner 1, the first indicationinformation is used to indicate the selected T₁ space-frequency vectorpairs in the M₁ space-frequency vector pairs by using the bitmap, andthe network device may determine the selected T₁ space-frequency vectorpairs based on a one-to-one correspondence between bits in the bitmapand the M₁ space-frequency vector pairs. In the manner 2, the firstindication information is used to indicate the T₁ space-frequency vectorpairs by using the index of the combination of the T₁ space-frequencyvector pairs in the M₁ space-frequency vector pairs, and the networkdevice may determine the T₁ space-frequency vector pairs based on thepredefined correspondence between a combination of space-frequencyvector pairs and an index. In the manner 3, the first indicationinformation is used to indicate the T₁ space-frequency vector pairs byusing the location of the beam vector included in each of the T₁space-frequency vector pairs and the location of the frequency domainvector included in each of the T₁ space-frequency vector pairs, and thenetwork device may determine the T₁ beam vectors and the T₁ frequencydomain vectors based on the location information of the beam vectors andthe location information of the frequency domain vectors, and furthercombine the T₁ beam vectors and the T₁ frequency domain vectors toobtain the T₁ space-frequency vector pairs.

Then, the network device may determine a quantized value of a weightingcoefficient of each space-frequency vector pair based on quantizedinformation of the weighting coefficient of each space-frequency vectorpair. As described above, the weighting coefficient of eachspace-frequency vector pair may be carried in the first indicationinformation or other information. For example, the network device maydetermine the quantized value of the weighting coefficient of eachspace-frequency vector pair based on a predefined one-to-onecorrespondence between a plurality of quantized values and a pluralityof indexes.

The space-frequency matrix is determined based on the T₁ space-frequencyvector pairs and the quantized value of the weighting coefficient ofeach space-frequency vector pair. For example, the network device maydetermine the space-frequency matrix based on the following formula:

${H = {\sum\limits_{t_{1} = 0}^{T_{1} - 1}{a_{t_{1}}u_{s,t_{1}}u_{f,t_{1}}^{\star}}}},{{{or}H} = {\sum\limits_{t_{1} = 0}^{T_{1} - 1}{a_{t_{1}}{u_{f,t_{1}} \otimes {u_{s,t_{1}}.}}}}}$

u_(s,t) ₁ represents a t₁ ^(th) beam vector in the T₁ beam vectors, andu_(f,t) ₁ represents a t₁ ^(th) frequency domain vector in the T₁frequency domain vectors. a_(t) ₁ represents a weighting coefficientcorresponding to a t₁ ^(th) space-frequency component matrix. Thespace-frequency matrix H in the formula may be the same as or similar tothe space-frequency matrix determined by the terminal device, and is aspace-frequency matrix restored by the network device based on the firstindication information. Because the space-frequency matrix may beobtained by constructing precoding vectors corresponding to the N_(f)frequency domain units, the network device may determine, based on ann_(f) ^(th) column vector in the matrix H, a precoding vectorcorresponding to an n_(f) ^(th) frequency domain unit.

Alternatively, the network device may generate the T₁ space-frequencycomponent matrices after determining the T₁ space-frequency vectorpairs. For example, a t₁ ^(th) space-frequency component matrix in theT₁ space-frequency component matrices may be denoted as U_(t) ₁ , whereU_(t) ₁ =u_(s,t) ₁ u_(f,t) ₁ *, U_(t) ₁ =u_(f,t) ₁ ⊗u_(s,t) ₁ , or thelike.

Then, the network device may determine the space-frequency matrix basedon the T₁ space-frequency component matrices and the quantized values ofthe weighting coefficients of the space-frequency component matrices.For example, the network device may determine the space-frequency matrixH based on the following formula:

$H = {\sum\limits_{t_{1} = 0}^{T_{1} - 1}{a_{t_{1}}{U_{t_{1}}.}}}$

Parameters in the formula have been described in detail above. Forbrevity, details are not described herein again.

The network device may determine, based on the space-frequency matrix, aprecoding vector corresponding to each frequency domain unit.

If the space-frequency matrix is a matrix whose dimension isN_(S)×N_(f), each column vector in the matrix may correspond to onefrequency domain unit, and may be used to determine a precoding vectorof the corresponding frequency domain unit. If the space-frequencymatrix is a vector whose length is N_(s)×N_(f), a column vector obtainedby sequentially connecting an (n_(f)×N_(s))^(th) element to an[(n_(f)+1)N_(s)−1] element in the vector may be a column vectorcorresponding to an n_(f) ^(th) frequency domain unit.

An n_(f) ^(th) column vector in the space-frequency matrix is used as anexample. The network device may perform normalization processing on then_(f) ^(th) column vector, to determine a precoding vector correspondingto the n_(f) ^(th) frequency domain unit. The normalization processingmay be, for example, multiplying the n_(f) ^(th) column vector by anormalization coefficient, so that a sum of powers of elements in thecolumn vector is equal to 1. A normalization coefficient may be, forexample, a reciprocal of a square root of a sum of moduli of theelements in the column. A specific value of the normalizationcoefficient and a specific manner of the normalization processing arenot limited in this application.

Optionally, the first indication information includes the locationinformation of the M₁ space-frequency component matrices and theinformation used to indicate the T₁ space-frequency component matrices.

As described above, the location information of the M₁ space-frequencycomponent matrices may be one-dimensional indexes of the M₁space-frequency component matrices, or may be two-dimensional indexes ofthe M₁ space-frequency component matrices.

If the location information of the M₁ space-frequency component matricesis one-dimensional indexes of the M₁ space-frequency component matrices,and a vector set pre-stored by the network device is a space-frequencycomponent matrix set, the network device may directly determine the M₁space-frequency component matrices in the space-frequency componentmatrix set based on the one-dimensional indexes.

If the location information of the M₁ space-frequency component matricesis one-dimensional indexes of the M₁ space-frequency component matrices,and vector sets pre-stored by the network device are a beam vector setand a frequency domain vector set, the network device may determine, inthe beam vector set and the frequency domain vector set based on apredefined rule for conversion between a one-dimensional index and atwo-dimensional index, the L₁ beam vectors and the K₁ frequency domainvectors that are used to generate the M₁ space-frequency componentmatrices.

If the location information of the M₁ space-frequency component matricesis two-dimensional indexes of the M₁ space-frequency component matrices,and vector sets pre-stored by the network device are a beam vector setand a frequency domain vector set, the network device may directlydetermine, in the beam vector set and the frequency domain vector setbased on the two-dimensional indexes, the L₁ beam vectors and the K₁frequency domain vectors that are used to generate the M₁space-frequency component matrices.

If the location information of the M₁ space-frequency component matricesis two-dimensional indexes of the M₁ space-frequency component matrices,and a vector set pre-stored by the network device is a space-frequencycomponent matrix set, the network device may determine the M₁space-frequency component matrices in the space-frequency componentmatrix set based on a predefined rule for conversion between aone-dimensional index and a two-dimensional index.

Then, the network device may further determine the T₁ space-frequencycomponent matrices in the M₁ space-frequency component matrices, and mayfurther determine the quantized values of the weighting coefficients ofthe space-frequency component matrices based on the quantizedinformation of the weighting coefficients of the space-frequencycomponent matrices.

A specific method for determining, by the network device, thespace-frequency matrix based on the T₁ space-frequency componentmatrices and the quantized values of the weighting coefficients of thespace-frequency component matrices has been described in detail above.For example, the network device may determine the space-frequency matrixbased on a formula

$H = {\sum\limits_{t_{1} = 0}^{T_{1} - 1}{a_{t_{1}}{U_{t_{1}}.}}}$

Then, the network device may determine the precoding vector of the oneor more frequency domain units. A specific method for determining, bythe network device, the precoding vector based on the space-frequencymatrix has described in detail above. For brevity, details are notdescribed herein again.

It should be understood that the foregoing listed two specific methodsfor determining the precoding vector of each frequency domain unit aremerely examples, and should not constitute any limitation on thisapplication. The network device may not generate the space-frequencymatrix, but directly determine the precoding vector of the one or morefrequency domain units based on the L₁ beam vectors and the K₁ frequencydomain vectors that are indicated by the terminal device.

For example, the network device may determine a precoding vector w_(n)_(f) of an n_(f) ^(th) frequency domain unit based on the followingformula:

$w_{n_{f}} = {{\frac{1}{P_{n_{f}}}\left\lbrack {\sum\limits_{t_{1} = 0}^{T_{1} - 1}{u_{s,t_{1}}a_{t_{1}}{\overset{\_}{u}}_{f,t_{1},n_{f}}}} \right\rbrack}.}$

$\frac{1}{P_{n_{f}}}$

is a normalization coefficient, P_(n) _(f) >0, u_(s,t) ₁ represents a t₁^(th) beam vector in the selected T₁ beam vectors, ū_(f,t,n) _(f)represents a conjugate of u_(f,t,n) _(f) , u_(f,t,n) _(f) represents ann_(f) ^(th) element in a t₁ ^(th) frequency domain vector u_(f,t) ₁ inthe selected T₁ frequency domain vectors, and a_(t) ₁ represents aweighting coefficient corresponding to the t₁ ^(th) beam vector u_(s,t)₁ and an n_(f) ^(th) element ū_(f,t) ₁ _(,n) _(f) in the t₁ ^(th)frequency domain vector u_(f,t) ₁ , where the weighting coefficient mayinclude, for example, an amplitude coefficient and a phase coefficient.

The foregoing formula may be further transformed into:

$w_{n_{f}} = {{\frac{1}{P_{n_{f}}}\left\lbrack {\sum\limits_{t_{1} = 0}^{T_{1} - 1}{v_{s,t_{1}}c_{t_{1}}{\overset{\_}{u}}_{f,t_{1},n_{f}}}} \right\rbrack}.}$

v_(s,t) ₁ is determined by the t₁ ^(th) beam vector in the selected T₁beam vectors and the wideband amplitude coefficient, and the weightingcoefficient c_(t) ₁ may satisfy a_(t) ₁ =p_(t) ₁ c_(t) ₁ .

It should be noted that, as described above, the length N_(f) of thefrequency domain vector may be a quantity of frequency domain unitsincluded in a frequency domain occupation bandwidth of a CSI measurementresource configured for the terminal device, or a signaling length of areporting band, or a quantity of to-be-reported frequency domain units.When the length of the frequency domain vector is the quantity offrequency domain units included in the frequency domain occupationbandwidth of the CSI measurement resource configured for the terminaldevice or the signaling length of the reporting band, the quantity ofto-be-reported frequency domain units may be less than or equal toN_(f). Therefore, the network device may determine a precoding vector ofeach frequency domain unit based on a location that is of ato-be-reported frequency domain unit and that is indicated by thereporting band or other signaling.

When the length of the frequency domain vector is determined based onthe quantity of frequency domain units included in the frequency domainoccupation bandwidth of the CSI measurement resource or the signalinglength of the reporting band, a change rule of a channel in a pluralityof consecutive frequency domain units may be reflected by using thefrequency domain vector. Compared with the method in which the length ofthe frequency domain vector is determined based on the quantity ofto-be-reported frequency domain units, this method ensures that thefrequency domain vector determined based on the quantity of frequencydomain units in the frequency domain occupation bandwidth of the CSImeasurement resource or the signaling length of the reporting band canmore accurately reflect a change rule of a channel in frequency domain,and a precoding vector restored based on feedback is also more adaptableto the channel.

It should be understood that the foregoing listed specific method inwhich the network device determines, based on the first indicationinformation, the precoding vector corresponding to the n_(f) ^(th)frequency domain unit is merely an example, and should not constituteany limitation on this application. This application does not exclude apossibility that the network device determines, based on the firstindication information in another manner, the precoding vectorcorresponding to the n_(f) ^(th) frequency domain unit.

Based on the foregoing technical solutions, the terminal deviceindicates a small quantity of beam vectors, frequency domain vectors,and space-frequency component matrices to the network device to help thenetwork device restore a precoding vector. The frequency domain vectormay be used to describe different change rules of a channel in frequencydomain. The terminal device may simulate a change of a channel infrequency domain through linear superposition of one or more frequencydomain vectors, so that a relationship between frequency domain units isfully explored, continuity of frequency domain is utilized, and a changerule on a plurality of frequency domain units is described by using arelatively small quantity of frequency domain vectors. Compared with thecurrent technology, this application does not require that a weightingcoefficient be independently reported based on each frequency domainunit, and an increase in frequency domain units does not causemultiplication of feedback overheads. Therefore, feedback overheads canbe greatly reduced while feedback precision is ensured.

However, because the beam vector set may include a relatively largequantity of beam vectors, and the frequency domain vector set mayinclude a relatively large quantity of frequency domain vectors, if arelatively small quantity of beam vectors and a relatively smallquantity of frequency domain vectors are directly indicated in the beamvector set and the frequency domain vector set, relatively high bitoverheads may be caused, or the terminal device and the network deviceneed to predefine a large quantity of correspondences between beamvector combinations and indexes and a large quantity of correspondencesbetween frequency domain vector combinations and indexes.

However, in this embodiment of this application, the terminal devicenarrows selection ranges of the beam vectors and the frequency domainvectors that are used for weighted summation to a range of the M₁space-frequency component matrices constructed by using the L₁ beamvectors and the K₁ frequency domain vectors. That is, the terminaldevice first selects a relatively small range of vectors from anexisting vector set, and then selects T₁ space-frequency componentmatrices from the range and indicates the T₁ space-frequency componentmatrices. On one hand, relatively high feedback overheads caused bydirectly indicating the T₁ space-frequency component matrices can beavoided. On the other hand, a large quantity of correspondences may notneed to be stored on both the terminal device and the network device.

A specific process in which the terminal device indicates a precodingvector in one polarization direction at one transport layer and thenetwork device determines the precoding vector is described above indetail with reference to FIG. 2 . However, it should be understood thatthe method is not only applicable to a case in which there is onetransport layer or one polarization direction, but also applicable to acase in which there are a plurality of transport layers or a pluralityof polarization directions.

For a same transport layer, T₁ space-frequency component matrices (or T₁space-frequency vector pairs) selected for a plurality of polarizationdirections may be the same. That is, same T₁ space-frequency componentmatrices (or T₁ space-frequency vector pairs) are shared in a pluralityof polarization directions, or different space-frequency componentmatrices (or space-frequency vector pairs) may be separately used in aplurality of polarization directions.

For ease of description below, a case in which there are a plurality ofpolarization directions or a plurality of transport layers is describedby using a space-frequency component matrix as an example. Thespace-frequency component matrix may include the foregoing listed matrixform or vector form. It may be understood that the space-frequencycomponent matrix is merely a possible form, and may also be representedin a form of a space-frequency vector pair. In other words, thespace-frequency component matrix in the following descriptions may alsobe replaced with a space-frequency vector pair.

Optionally, the first indication information is used to indicate aprecoding vector of each frequency domain unit in one or morepolarization directions.

When a plurality of polarization directions share same T₁space-frequency component matrices, L₁ beam vectors and K₁ frequencydomain vectors that are used to determine the T₁ space-frequencycomponent matrices may also be shared in the plurality of polarizationdirections. In this case, in the plurality of pieces of first indicationinformation corresponding to the plurality of polarization directions,information used to indicate the L₁ beam vectors, the K₁ frequencydomain vectors, and the T₁ space-frequency component matrices may beshared. For example, the terminal device may use a bitmap whose lengthis L₁×K₁ to indicate T₁ space-frequency component matrices used in eachof the plurality of polarization directions.

If the first indication information is used only to indicate the L₁ beamvectors, the K₁ frequency domain vectors, and the T₁ space-frequencycomponent matrices, the terminal device may generate and send only onepiece of first indication information for a plurality of polarizationdirections. If the first indication information is further used toindicate weighting coefficients of the T₁ space-frequency componentmatrices, the terminal device may send one piece of first indicationinformation for each polarization direction. Because in the plurality ofpieces of first indication information corresponding to the plurality ofpolarization directions, the information used to indicate the L₁ beamvectors, the K₁ frequency domain vectors, and the T₁ space-frequencycomponent matrices may be shared, the terminal device may indicate theL₁ beam vectors, the K₁ frequency domain vectors, and the T₁space-frequency component matrices only once, and weighting coefficientsof space-frequency component matrices that correspond to differentpolarization directions may be separately indicated by using differentfirst indication information. For brevity, descriptions of a same orsimilar case are omitted below.

The terminal device may use, in a plurality of polarization directions,L₁ beam vectors, K₁ frequency domain vectors, and T₁ space-frequencycomponent matrices that are determined based on a polarizationdirection. A specific polarization direction based on which the terminaldevice determines the L₁ beam vectors, the K₁ frequency domain vectors,and the T₁ space-frequency component matrices may be predefined, forexample, defined in a protocol. This is not limited in this application.

Alternatively, the terminal device may determine T₁ space-frequencycomponent matrices based on each polarization direction, to obtain aplurality of groups of space-frequency component matrices. The terminaldevice selects a group of space-frequency component matrices from theplurality of groups of space-frequency component matrices for use in aplurality of polarization directions. A sum of moduli of weightingcoefficients of the selected group of space-frequency component matricesmay be greater than or equal to a sum of moduli of weightingcoefficients of any group of space-frequency component matrices in oneor more remaining groups of space-frequency component matrices.

When different space-frequency component matrices are separately used ina plurality of polarization directions, quantities of space-frequencycomponent matrices used in the different polarization directions may bethe same or may be different. Quantities of beam vectors used todetermine space-frequency component matrices in all polarizationdirections may be the same or may be different, and quantities offrequency domain vectors used to determine the space-frequency componentmatrices in all the polarization directions may be the same or may bedifferent. These are not limited in this application. In this case, inthe plurality of pieces of first indication information corresponding tothe plurality of polarization directions, information that is about beamvectors, frequency domain vectors, and space-frequency componentmatrices and that corresponds to different polarization directions maybe different from each other. The terminal device may separatelyindicate, based on each polarization direction, a selected beam vector,a selected frequency domain vector, and a space-frequency componentmatrix used for weighted summation. A specific manner in which theterminal device determines, based on each polarization direction, thebeam vector, the frequency domain vector, and the space-frequencycomponent matrix used for weighted summation is the same as theforegoing specific manner in which the L₁ beam vectors, the K₁ frequencydomain vectors, and the T₁ space-frequency component matrices aredetermined based on one polarization direction. For brevity, details arenot described herein again.

Generally, same L₁ beam vectors, same K₁ frequency domain vectors, andsame T₁ space-frequency component matrix may be shared in a plurality ofpolarization directions. An example in which a plurality of polarizationdirections share same L₁ beam vectors, same K₁ frequency domain vectors,and same T₁ space-frequency component matrices is used below fordescription.

It is assumed that a quantity of polarization directions is 2, and sameL₁ beam vectors and same K₁ frequency domain vectors are shared in thetwo polarization directions. T₁ space-frequency component matrices usedfor weighted summation in the two polarization directions are also thesame.

The network device may determine a precoding vector of an n_(f) ^(th)frequency domain unit based on the following formula:

$w_{n_{f}} = {{\frac{1}{P_{n_{f}}}\begin{bmatrix}{\sum\limits_{t_{1} = 0}^{T_{1} - 1}{u_{s,t_{1}}a_{t_{1}}{\overset{\_}{u}}_{f,t_{1},n_{f}}}} \\{\sum\limits_{t_{1} = 0}^{T_{1} - 1}{u_{s,t_{1}}a_{t_{1} + T_{1}}{\overset{\_}{u}}_{f,t_{1},n_{f}}}}\end{bmatrix}}.}$

a_(t) ₁ represents a weighting coefficient corresponding to a t₁ ^(th)beam vector and an n_(f) ^(th) element in the t₁ ^(th) frequency domainvector u_(f,t) ₁ in a first polarization direction, and a_(t) ₁ _(+T) ₁represents a weighting coefficient corresponding to the t₁ ^(th) beamvector u_(f,t) ₁ and an n_(f) ^(th) element ū_(f,t) ₁ _(,n) _(f) in thet₁ ^(th) frequency domain vector u_(f,t) ₁ in a second polarizationdirection.

The foregoing formula may be further transformed into:

$w_{n_{f}} = {{\frac{1}{P_{n_{f}}}\begin{bmatrix}{\sum\limits_{t_{1} = 0}^{T_{1} - 1}{v_{s,t_{1}}c_{t_{1}}{\overset{\_}{u}}_{f,t_{1},n_{f}}}} \\{\sum\limits_{t_{1} = 0}^{T_{1} - 1}{v_{s,{t_{1} + T}}c_{t_{1} + T_{1}}{\overset{\_}{u}}_{f,t_{1},n_{f}}}}\end{bmatrix}}.}$

v_(s,t) ₁ is determined based on the t₁ ^(th) beam vector in theselected T₁ beam vectors in the first polarization direction and thewideband amplitude coefficient p_(t) ₁ , v_(s,t) ₁ _(+T) is determinedbased on the t₁ ^(th) beam vector in the selected T₁ beam vectors in thesecond polarization direction and the wideband amplitude coefficientp_(t) ₁ _(+T), a_(t) ₁ represents a weighting coefficient correspondingto v_(s,t) ₁ and an n_(f) ^(th) element in the t₁ ^(th) frequency domainvector u_(f,t) ₁ in the first polarization direction, and a_(t) ₁ _(+T)₁ represents a weighting coefficient corresponding to v_(s,t) ₁ _(+T)and an n_(f) ^(th) element ū_(f,t) ₁ _(,n) _(f) in the t₁ ^(th)frequency domain vector u_(f,t) ₁ in the second polarization direction.

Optionally, the two polarization directions share the same L₁ beamvectors, K₁ frequency domain vectors, and T₁ space-frequency componentmatrices. When the terminal device uses the bitmap in the manner 1 toindicate the T₁ space-frequency component matrices, specifically, abitmap whose length is L₁×K₁ may be used for indication.

Optionally, the two polarization directions share the same L₁ beamvectors and K₁ frequency domain vectors. The terminal device maydetermine one or more space-frequency component matrices in eachpolarization direction based on the L₁ beam vectors and the K₁ frequencydomain vectors. A total quantity of space-frequency component matricesdetermined in the two polarization directions may be denoted as, forexample, S₁. A value of S₁ may be 2T₁, and the terminal device mayseparately determine T₁ relatively strong space-frequency componentmatrices in each polarization direction. T₁ space-frequency componentmatrices in the first polarization direction in the two polarizationdirections may be the same as or different from T₁ space-frequencycomponent matrices in the second polarization direction in the twopolarization directions. This is not limited in this application.Alternatively, a value of S₁ may not be 2T₁, and the terminal device maydetermine S₁ relatively strong space-frequency component matricesjointly based on the two polarization directions. When the terminaldevice determines the S₁ relatively strong space-frequency componentmatrices jointly based on the two polarization directions, a totalquantity of space-frequency component matrices in the first polarizationdirection and the second polarization direction may be S₁. In addition,a quantity of space-frequency component matrices in the firstpolarization direction may be the same as or different from a quantityof space-frequency component matrices in the second polarizationdirection. This is not limited in this application.

When indicating the S₁ space-frequency component matrices, the terminaldevice may indicate the S₁ space-frequency component matrices still byusing any one of the manner 1 to the manner 4 listed above. When thebitmap in the manner 1 is used for indication, a length of the bitmapmay be 2L₁×K₁ bits. Alternatively, bitmaps corresponding to twopolarization directions may be separately used for indication.

Optionally, when the quantity of polarization directions is 2, the thirdindication information may also be used to indicate the value of S₁.

If the terminal device determines and reports space-frequency componentmatrices based on each polarization direction, S₁ may be an even number,for example, 2T₁. If the terminal device determines and reportsspace-frequency component matrices jointly based on the two polarizationdirections, S₁ may be an odd number or an even number. This is notlimited in this application.

Optionally, the two polarization directions share the same L₁ beamvectors, and the terminal device may determine the K₁ frequency domainvectors and the T₁ space-frequency component matrices based on eachpolarization direction.

Optionally, the two polarization directions share the same L₁ beamvectors, and the terminal device may determine the K₁ frequency domainvectors based on each polarization direction, and determine 2T₁relatively strong space-frequency component matrices jointly based onthe two polarization directions.

Optionally, the T₁ space-frequency component matrices indicated by usingthe first indication information are associated with a first transportlayer in the plurality of transport layers. In other words, the T₁space-frequency component matrices indicated by using the firstindication information may be used to determine a precoding vector ofone or more frequency domain units at the first transport layer.

The first transport layer may be one transport layer, or may be aplurality of transport layers. This is not limited in this application.In other words, the first indication information may be used todetermine a precoding vector of each frequency domain unit at the one ormore transport layers.

In conclusion, the first indication information may be used to indicateone or more polarization directions and/or a precoding vector of eachfrequency domain unit at the one or more transport layers. To bespecific, the first indication information may be used to determine aprecoding vector of each frequency domain unit in the one or morepolarization directions, may be used to determine a precoding vector ofeach frequency domain unit at the one or more transport layers, or maybe used to determine a precoding vector of each frequency domain unit inthe one or more polarization directions at each of the one or moretransport layers.

Further, the method further includes: The terminal device generatesfourth indication information, where the fourth indication informationis used to indicate L₂ beam vectors in the beam vector set, K₂ frequencydomain vectors in the frequency domain vector set, and T₂space-frequency component matrices. A weighted sum of the T₂space-frequency component matrices may be used to determine a precodingvector of one or more frequency domain units at a second transportlayer. In other words, the L₂ beam vectors, the K₂ frequency domainvectors, and the T₂ space-frequency component matrices that areindicated by using the fourth indication information are associated withthe second transport layer.

Optionally, the fourth indication information is used to indicate L₂beam vectors and T₂ space-frequency component matrices, and a weightedsum of the T₂ space-frequency component matrices is used to determine aprecoding vector of one or more frequency domain units. The L₂ beamvectors and the K₂ frequency domain vectors correspond to M₂space-frequency component matrices, the T₂ space-frequency componentmatrices are a part of the M₂ space-frequency component matrices, eachof the M₂ space-frequency component matrices is uniquely determined byone of the L₂ beam vectors and one of the K₂ frequency domain vectors,and M₂=L₂×K₂; the L₂ beam vectors are a part of beam vectors in the beamvector set, and/or the K₂ frequency domain vectors are a part offrequency domain vectors in the frequency domain vector set; and M₂, L₂,K₂, and T₂ are all positive integers.

Optionally, the K₂ frequency domain vectors are preconfigured. Forexample, the K₂ frequency domain vectors may be all or a part offrequency domain vectors in the frequency domain vector set.

For example, K₂=K₀ may be predefined in the protocol. That is, in theprotocol, a universal set of the frequency domain vector set is used asthe K₂ frequency domain vectors by default. For another example, thevalue of K₂ may be predefined in the protocol, and frequency domainvectors in the frequency domain vector set that are used as the K₂frequency domain vectors may be specified in advance. For still anotherexample, the value of K₂ may be predefined in the protocol, and the K₂frequency domain vectors may be indicated by the network device inadvance by using signaling.

In other words, it may be predefined that the terminal device does notneed to report the K₂ frequency domain vectors. The K₂ frequency domainvectors may be specified in advance, for example, defined in a protocolor configured by the network device. This is not limited in thisapplication.

Optionally, the K₂ frequency domain vectors are the same as the K₁frequency domain vectors. Optionally, the K₂ frequency domain vectorsare different from the K₁ frequency domain vectors.

Optionally, the K₂ frequency domain vectors are a subset of the K₁frequency domain vectors.

The foregoing has described in detail, with reference to the firstindication information, different parameter values and vectors reportedby the terminal device when different parameters are configured. Whengenerating and sending the fourth indication information, the terminaldevice may perform processing in a manner the same as that describedabove. For brevity, details are not described herein again.

Optionally, the second transport layer is one or more transport layersother than the first transport layer in a plurality of transport layers.In other words, the fourth indication information may be used todetermine a precoding vector of each frequency domain unit at the one ormore transport layers. Specifically, the fourth indication informationmay be used to indicate a precoding vector of each frequency domain unitin one or more polarization directions at each of the second transportlayers.

In a possible design, L₁=L₂, K₁=K₂, and T₁=T₂. In other words, for aplurality of transport layers, quantities of beam vectors determined atany two transport layers are the same, quantities of frequency domainvectors determined at any two transport layers are the same, andquantities of space-frequency component matrices determined at any twotransport layers are the same.

In this design, optionally, the transport layers may share the same L₁beam vectors, the same K₁ frequency domain vectors, and the same T₁space-frequency component matrices. In this case, the fourth indicationinformation may be the same as the information that is used to indicatethe L₁ beam vectors, the K₁ frequency domain vectors, and the T₁space-frequency component matrices and that is in the first indicationinformation. In this case, the first indication information and thefourth indication information may be same indication information.

In addition, when the foregoing information is shared by differenttransport layers and/or different polarization directions, only onepiece of indication information may be generated and sent.

Optionally, the transport layers may share the same L₁ beam vectors andK₁ frequency domain vectors, but use respective T₁ space-frequencycomponent matrices. In other words, the T₁ space-frequency componentmatrices at the first transport layer are different from the T₁space-frequency component matrices at the second transport layer. Inthis case, the fourth indication information may be the same as theinformation used to indicate the L₁ beam vectors and the K₁ frequencydomain vectors in the first indication information, and the firstindication information and the fourth indication information may be usedto indicate T₁ space-frequency component matrices at correspondingtransport layers.

Optionally, each transport layer uses its own L₁ beam vectors, K₁frequency domain vectors, or T₁ space-frequency component matrices. Inother words, the L₁ beam vectors at the first transport layer aredifferent from the L₁ beam vectors at the second transport layer, the K₁frequency domain vectors at the first transport layer are different fromthe K₁ frequency domain vectors at the second transport layer, and theT₁ space-frequency component matrices at the first transport layer aredifferent from the T₁ space-frequency component matrices at the secondtransport layer. In this case, the first indication information and thesecond indication information may be used to indicate the L₁ beamvectors, the K₁ frequency domain vectors, and the T₁ space-frequencycomponent matrices that are at the corresponding transport layers.

Further, values of L₁, K₁, and T₁ may vary with an increase of thequantity of transport layers. For example, it may be predefined in aprotocol that when the quantity of transport layers is greater than apreset threshold, at least one of L₁, K₁, and T₁ is decreased.

For example, when the quantity of transport layers is greater than 2, T₁may be decreased. For example, T₁ may be decreased to T₁/2 or T₁/3.

For another example, when the quantity of transport layers is greaterthan 2, both L₁ and T₁ may be decreased. For example, L₁ may bedecreased to L₁/2, and T₁ may be decreased to T₁/2; or L₁ may bedecreased to L₁/3, and T₁ may be decreased to T₁/3.

For still another example, when the quantity of transport layers isgreater than 2, both K₁ and T₁ may be decreased. For example, K₁ may bedecreased to K₁/2, and T₁ may be decreased to T₁/2; or K₁ may bedecreased to K₁/3, and T₁ may be decreased to T₁/3.

For yet another example, when the quantity of transport layers isgreater than 2, all of L₁, K₁ and T₁ may be decreased. For example, L₁may be decreased to L₁/2, K₁ may be decreased to K₁/2, and T₁ may bedecreased to T₁/2; or L₁ may be decreased to L₁/3, K₁ may be decreasedto K₁/3, and T₁ may be decreased to T₁/3.

It should be understood that the foregoing listed preset threshold ismerely an example, and should not constitute any limitation on thisapplication. It should be further understood that the foregoing listedmethods for decreasing L₁, K₁, and T₁ are merely examples, and shouldnot constitute any limitation on this application. The foregoing presetthreshold and specific values obtained after L₁, K₁, and T₁ aredecreased may be predefined in a protocol.

It should be noted that although values of L₁, K₁, and T₁ may vary withthe quantity of transport layers, L₁, K₁, and T₁ that are obtained aftera change and L₂, K₂, and T₂ that are obtained after a change may stillsatisfy L₁=L₂, K₁=K₂, and T₁=T₂.

It should be further understood that although the first transport layerand the second transport layer are used as examples above to describevalue relationships between L₁ and L₂, K₁ and K₂, and T₁ and T₂ atdifferent transport layers, this should not constitute any limitation onthis application. The quantity of transport layers is not limited to 2,and may be greater than 2. For example, the quantity of transport layersis 3, 4, or the like. This is not limited in this application.

In another possible design, L₁>L₂, K₁>K₂, and T₁>T₂. In other words, fora plurality of transport layers, quantities of beam vectors determinedat at least two transport layers are different, quantities of frequencydomain vectors determined at at least two transport layers aredifferent, or quantities of space-frequency component matricesdetermined at at least two transport layers are different.

Optionally, when the quantity of transport layers is greater than apreset threshold, at least one of a quantity of space-frequencycomponent matrices, a quantity of beam vectors, and a quantity offrequency domain vectors at some transport layers may be decreased.

For example, when the quantity of transport layers is greater than thepreset threshold, the quantity of space-frequency component matrices atthe some transport layers may be halved. In other words, the quantity T₁of the space-frequency component matrices at the first transport layermay be twice the quantity T₂ of the space-frequency component matricesat the second transport layer. The first transport layer may correspondto, for example, a precoding vector determined based on an eigenvectorcorresponding to a larger eigenvalue in an SVD process, and the secondtransport layer may correspond to, for example, a precoding vectordetermined based on an eigenvector corresponding to a smaller eigenvaluein the SVD process. The first transport layer may indicate one transportlayer, or may indicate a plurality of transport layers with a samecharacteristic. The second transport layer may indicate one transportlayer, or may indicate a plurality of transport layers with a samecharacteristic.

When the first transport layer indicates a plurality of transportlayers, there may be a plurality of pieces of first indicationinformation used to indicate precoding vectors of the first transportlayers, to correspond to the plurality of transport layers. If theplurality of transport layers share a beam vector, a frequency domainvector, and a space-frequency component matrix, information used toindicate the beam vector, the frequency domain vector, and thespace-frequency component matrix in the plurality of pieces of firstindication information may be shared. In this case, only one piece offirst indication information may be generated and sent.

Likewise, when the second transport layer indicates a plurality oftransport layers, there may be a plurality of pieces of fourthindication information used to indicate precoding vectors of the secondtransport layers, to correspond to the plurality of transport layers. Ifthe plurality of transport layers share a beam vector, a frequencydomain vector, or a space-frequency component matrix, information usedto indicate the beam vector, the frequency domain vector, or thespace-frequency component matrix in the plurality of pieces of fourthindication information may be shared. In this case, only one piece offourth indication information may be generated and sent.

The foregoing division of the transport layers based on the eigenvalueis merely a possible implementation, and should not constitute anylimitation on this application. For example, another criterion fordividing the transport layers may be predefined in a protocol. This isnot limited in this application.

For example, the quantity of transport layers is 4, and the presetthreshold is 2. In this case, quantities of space-frequency componentmatrices at a 2^(nd) transport layer and a 3^(rd) transport layer in thefour transport layers may be halved, and quantities of space-frequencycomponent matrices at a 0^(th) transport layer and a 1^(st) transportlayer remain unchanged. The 0^(th) transport layer and the 1^(st)transport layer may be two examples of the first transport layer, andthe 2^(nd) transport layer and the 3^(rd) transport layer may be twoexamples of the second transport layer.

Based on the same manner, a quantity of beam vectors and/or a quantityof frequency domain vectors at some transport layers may also bedecreased. For brevity, examples are not further listed one by oneherein.

Still further, when the quantity of transport layers is greater than thepreset threshold, and at least one of the quantity of space-frequencycomponent matrices, the quantity of beam vectors, and the quantity offrequency domain vectors at some transport layers is decreased, theterminal device may use, at the second transport layer, somespace-frequency component matrices that are at the first transportlayer. In this case, the terminal device may indicate, in the fourthindication information by using, for example, a bitmap or an index of aspace-frequency component matrix, only some space-frequency componentmatrices used at the second transport layer, and does not repeatedlyindicate the selected beam vector and the selected frequency domainvector. Therefore, feedback overheads can be reduced. In this case, theterminal device may indicate a relative location, in space-frequencycomponent matrices used at the first transport layer, of the somespace-frequency component matrices used at the second transport layer,where the relative location is referred to as a local (local) location,such as a relative number or a relative index.

It may be understood that, when quantities of beam vectors at at leasttwo transport layers are different, or quantities of frequency domainvectors determined at at least two transport layers are different, orquantities of space-frequency component matrices determined at at leasttwo transport layers are different, the terminal device may separatelyindicate, by using the first indication information and the fourthindication information, selected beam vectors, selected frequency domainvectors, and selected space-frequency component matrices that are at thecorresponding transport layer, and weighting coefficient of thespace-frequency component matrices.

It should be understood that the foregoing methods may be used incombination. For example, the quantity of transport layers is 4, andboth a 0^(th) transport layer and a 1^(st) transport layer may be firsttransport layers. The 0^(th) transport layer and the 1^(st) transportlayer may share a same beam vector and a same frequency domain vector.When two pieces of first indication information corresponding to the0^(th) transport layer and the 1^(st) transport layer are used toindicate beam vectors and frequency domain vectors at the 0^(th)transport layer and the 1^(st) transport layer, only indicationinformation for indicating L₁ beam vectors once and indicationinformation for indicating K₁ frequency domain vectors once may begenerated. However, space-frequency component matrices used at the0^(th) transport layer and the 1^(st) transport layer may be separatelyindicated by using different bitmaps. The first indication informationcorresponding to the 0^(th) transport layer may include a bitmap used toindicate the space-frequency component matrix that is for the 0^(th)transport layer. The first indication information corresponding to the1^(st) transport layer may include a bitmap used to indicate thespace-frequency component matrix that is for the 1^(st) transport layer.

Both the 2^(nd) transport layer and the 3^(rd) transport layer may besecond transport layers. The 2^(nd) transport layer and the 3^(rd)transport layer may also share a same beam vector and a same frequencydomain vector, beam vectors used at the 2^(nd) transport layer and the3^(rd) transport layer may be a subset of the beam vectors used at the0^(th) transport layer and the 1^(st) transport layer, and frequencydomain vectors used at the 2^(nd) transport layer and the 3^(rd)transport layer may also be a subset of the frequency domain vectorsused at the 0^(th) transport layer and the 1^(st) transport layer.Certainly, the beam vectors used at the 2^(nd) transport layer and the3^(rd) transport layer may alternatively be determined by the terminaldevice based on the 2^(nd) transport layer and/or the 3^(rd) transportlayer, and are not necessarily a subset of the beam vectors used at the0^(th) transport layer and the 1^(st) transport layer. The frequencydomain vectors used at the 2^(nd) transport layer and the 3^(rd)transport layer may alternatively be determined by the terminal devicebased on the 2^(nd) transport layer and/or the 3^(rd) transport layer,and are not necessarily a subset of the frequency domain vectors used atthe 0^(th) transport layer and the 1^(st) transport layer. This is notlimited in this application.

When the beam vectors used at the 2^(nd) transport layer and the 3^(rd)transport layer are a subset of the beam vectors used at the 0^(th)transport layer and the 1^(st) transport layer, and the frequency domainvectors used by the 2^(nd) transport layer and the 3^(rd) transportlayer are a subset of the frequency domain vectors used at the 0^(th)transport layer and the 1^(st) transport layer; when two pieces offourth indication information respectively corresponding to the 2^(nd)transport layer and the 3^(rd) transport layer are used to indicate thebeam vectors and the frequency domain vectors of the 2^(nd) transportlayer and the 3^(rd) transport layer, only indication information forindicating L₂ beam vectors and K₂ frequency domain vectors once may begenerated. The L₂ beam vectors and the K₂ frequency domain vectors maybe indicated in the L₁ beam vectors and the K₁ frequency domain vectors.For example, relative locations of the L₂ beam vectors in the L₁ beamvectors may be indicated, and relative locations of the K₂ frequencydomain vectors in the K₁ frequency domain vectors may be indicated.However, space-frequency component matrices used at the 2^(nd) transportlayer and the 3^(rd) transport layer may be separately indicated byusing different bitmaps. The fourth indication information correspondingto the 2^(nd) transport layer may include a bitmap used to indicate thespace-frequency component matrix that is for the 2^(nd) transport layer.The fourth indication information corresponding to the 3^(rd) transportlayer may include a bitmap used to indicate the space-frequencycomponent matrix that is for the 3^(rd) transport layer.

It should be noted that because the quantity of transport layers may bedetermined by the terminal device, when the network device indicates L₁,K₁, and T₁ by using higher layer signaling, the quantity of transportlayers cannot be determined in advance. Therefore, the network devicemay separately indicate one value for at least two of L₁, K₁, and T₁,and the terminal device may determine, based on the quantity oftransport layers and a predefined rule, whether a value of L₁, K₁, or T₁needs to be changed.

It is assumed that a quantity of transport layers is R, and a quantityof polarization directions is 2. The network device may determine aprecoding vector of an n_(f) ^(th) frequency domain unit at an r^(th)transport layer based on the following formula:

$w_{r,n_{f}} = {{\frac{1}{P_{r,n_{f}}}\begin{bmatrix}{\sum\limits_{t_{1} = 0}^{T_{1} - 1}{u_{s,r,t_{1}}a_{r,t_{1}}{\overset{\_}{u}}_{f,r,t_{1},n_{f}}}} \\{\sum\limits_{t_{1} = 0}^{T_{1} - 1}{u_{s,r,t_{1}}a_{r,{t_{1} + T_{1}}}{\overset{\_}{u}}_{f,r,t_{1},n_{f}}}}\end{bmatrix}}.}$

$\frac{1}{P_{r,n_{f}}}$

is a normalization coefficient corresponding to the r^(th) transportlayer, P_(r,n) _(t) >0, u_(s,r,t) ₁ is a t₁ ^(th) beam vector at ther^(th) transport layer, ū_(f,r,t) ₁ _(,n) _(f) is an n_(f) ^(th) elementin a t₁ ^(th) frequency domain vector u_(f,r,t) ₁ at the r^(th)transport layer, a_(r,t) ₁ represents a weighting coefficientcorresponding to a t₁ ^(th) beam vector u_(s,r,t) ₁ and an n_(f) ^(th)element ū_(f,r,t) ₁ _(,n) _(f) in a t₁ ^(th) frequency domain vectoru_(f,r,t) ₁ in a first polarization direction at the r^(th) transportlayer, and a_(r,t) ₁ _(+T) ₁ represents a weighting coefficientcorresponding to a t₁ ^(th) beam vector u_(s,r,t) ₁ and an n_(f) ^(th)element ū_(f,r,t) ₁ _(,n) _(f) in a t₁ ^(th) frequency domain vectoru_(f,r,t) ₁ in a second polarization direction at the r^(th) transportlayer.

If the same L₁ beam vectors and K₁ frequency domain vectors are sharedat each transport layer, the foregoing formula may be simplified as:

$w_{r,n_{f}} = {{\frac{1}{P_{r,n_{f}}}\begin{bmatrix}{\sum\limits_{t_{1} = 0}^{T_{1} - 1}{u_{s,t_{1}}a_{r,t_{1}}{\overset{\_}{u}}_{f,t_{1},n_{f}}}} \\{\sum\limits_{t_{1} = 0}^{T_{1} - 1}{u_{s,t_{1}}a_{r,{t_{1} + T_{1}}}{\overset{\_}{u}}_{f,t_{1},n_{f}}}}\end{bmatrix}}.}$

Still further, the network device may determine a precoding matrix of ann_(f) ^(th) frequency domain unit based on the following formula:

$W_{n_{f}} = {\frac{1}{P_{n_{f}}}\left\lbrack {\begin{matrix}w_{0,n_{f}} & \ldots & \left. w_{{R - 1},n_{f}} \right\rbrack\end{matrix}.} \right.}$

w_(0,n) _(f) represents a precoding vector of an n_(f) ^(th) frequencydomain unit at a 0^(th) transport layer, and w_(0,n) _(f) represents aprecoding vector of an n_(f) ^(th) frequency domain unit at an(R−1)^(th) transport layer.

Based on the foregoing technical solutions, the terminal device mayindicate the precoding matrix of the one or more frequency domain unitsat the one or more transport layers to the network device.

Therefore, the terminal device indicates a small quantity of beamvectors, frequency domain vectors, and space-frequency componentmatrices to the network device to help the network device restore aprecoding vector. The frequency domain vector may be used to describedifferent change rules of a channel in frequency domain. The terminaldevice may simulate a change of a channel in frequency domain throughlinear superposition of one or more frequency domain vectors, so that arelationship between frequency domain units is fully explored,continuity of frequency domain is utilized, and a change rule on aplurality of frequency domain units is described by using a relativelysmall quantity of frequency domain vectors. Compared with the currenttechnology, this application does not require that a weightingcoefficient be independently reported based on each frequency domainunit, and an increase in frequency domain units does not causemultiplication of feedback overheads. Therefore, feedback overheads canbe greatly reduced while feedback precision is ensured.

It should be understood that the method for indicating a precodingvector provided above is merely a possible implementation, and shouldnot constitute any limitation on this application. For example, afterdetermining the L₁ beam vectors and the K₁ frequency domain vectors, theterminal device may feed back weighting coefficients separately for theM₁ space-frequency component matrices corresponding to the L₁ beamvectors and the K₁ frequency domain vectors. The terminal device may userelatively high feedback precision for the weighting coefficients of theT₁ space-frequency component matrices in the M₁ space-frequencycomponent matrices, and use relatively low feedback precision forweighting coefficients of the remaining M₁-T₁ space-frequency componentmatrices, to reduce feedback overheads. Specifically, a quantity ofquantized bits of a weighting coefficient of any one of the T₁space-frequency component matrices may be greater than a quantity ofquantized bits of a weighting coefficient of any one of the remainingM₁-T₁ space-frequency component matrices. Although the caused feedbackoverheads are slightly higher than the feedback overheads caused by themethod provided above, the precoding matrix restored by the networkdevice may be closer to the precoding matrix determined by the terminaldevice. Therefore, approximation precision is higher.

It should be noted that the method for indicating and determining aprecoding matrix provided above is particularly applicable to a case inwhich there are a large quantity of consecutive frequency domain units.In this method, correlation between the frequency domain units can befully used, and feedback overheads can be reduced, thereby reducing hugeoverheads caused by independent feedback of a plurality of frequencydomain units.

However, in some cases, there are a few of frequency domain unit, orfrequency domain units are inconsecutive. If an existing manner ofindependently feeding back each frequency domain unit is used toindicate a precoding vector of each frequency domain unit, relativelylow feedback overheads may be caused. In addition, in a case in whichthe frequency domain units are inconsecutive, relatively highapproximate precision can be ensured through independent feedback ofeach frequency domain unit. Therefore, this application further providesa PMI feedback method, so that a precoding vector can be fed back in afeedback mode with reference to different scenarios, thereby ensuringapproximate precision and reducing feedback overheads.

The following describes in detail a PMI feedback method according toanother embodiment of this application with reference to FIG. 3 .

FIG. 3 is a schematic flowchart of a PMI feedback method 300 from adevice interaction perspective according to another embodiment of thisapplication. As shown in the figure, the method 300 may include step 310to step 340. The following describes each step in the method 300 indetail.

It should be noted that, in this embodiment, a terminal device mayindicate a precoding matrix to a network device by using a PMI. The PMImay include the first indication information and/or the fourthindication information in the foregoing method 200, and may furtherinclude other information that is used to indicate a precoding matrixand that is different from the first indication information and thefourth indication information. This is not limited in this application.In addition, the PMI is merely a name of information used to indicate aprecoding matrix, and should not constitute any limitation on thisapplication. This application does not exclude a possibility thatanother name is defined in a future protocol to represent a functionthat is the same as or similar to that of the PMI.

In step 310, the network device generates sixth indication information,where the sixth indication information is used to indicate a PMIfeedback mode.

In this embodiment, the PMI feedback mode may be the feedback modeprovided above, or may be another feedback mode. Specifically, the PMIfeedback mode may be a first feedback mode or a second feedback mode.The first feedback mode may be a mode in which a PMI is fed back basedon only a beam vector set. The second feedback mode may be a mode inwhich a PMI is fed back based on a beam vector set and a frequencydomain vector set, or may be a mode in which a PMI is fed back based ona space-frequency component matrix set.

Because the space-frequency component matrix set is associated with thebeam vector set and the frequency domain vector set, in the secondfeedback mode, feeding back the PMI based on the beam vector set and thefrequency domain vector set may be considered as being equivalent tofeeding back the PMI based on the space-frequency component matrix set.In addition, because the beam vector set and the frequency domain vectorset may be converted into the space-frequency component matrix set, orvice versa, it may be further considered that the second feedback modeis feeding back the PMI based on the beam vector set and thespace-frequency component matrix set, or feeding back the PMI based onthe frequency domain vector set and the space-frequency component matrixset. This is not limited in this application.

That the PMI is fed back only based on the beam vector set in the firstfeedback mode is relative to the second feedback mode. Compared with thesecond feedback mode, the first feedback mode ensures that the PMI maybe fed back based on only the beam vector set, and no additional vectorset or matrix set needs to be provided. In other words, a differencebetween the first feedback mode and the second feedback mode lies inthat the first feedback mode is not based on a frequency domain vectorset, but the second feedback mode is based on a frequency domain vectorset.

From another perspective, the first feedback mode may be afrequency-domain-unit-independent feedback mode, and the second feedbackmode may be a frequency-domain-unit-joint feedback mode.

In a possible implementation, for example, for the first feedback mode,refer to a feedback mode in which a PMI is fed back based on a type IIcodebook and that is defined in the NR protocol TS38.214 R15. The secondfeedback mode may be, for example, the feedback mode described abovewith reference to the method 200. Compared with the first feedback mode,the second feedback mode may be understood as afrequency-domain-unit-joint feedback mode. It can be learned from theforegoing descriptions that, in the second feedback mode, based oncontinuity in frequency domain, a plurality of frequency domain unitsare jointly fed back by using a relationship between the frequencydomain units, to reduce frequency domain feedback overheads. Especiallywhen there are a relatively large quantity of to-be-reported frequencydomain units, compared with the first feedback mode, the second feedbackmode can greatly reduce feedback overheads.

In this embodiment, the sixth indication information may be used toexplicitly indicate the feedback mode. For example, an indication bit oran indication field may be used to indicate the feedback mode. Forexample, when the indication bit is set to “0”, it indicates that thefirst feedback mode is used; when the indication bit is set to “1”, itindicates that the second feedback mode is used. Alternatively, when theindication bit is set to “1”, it indicates that the first feedback modeis used; when the indication bit is set to “0”, it indicates that thesecond feedback mode is used. This is not limited in this application.

The sixth indication information may also be used to implicitly indicatethe feedback mode by using other information. For example, when thenetwork device indicates a length of a frequency domain vector to theterminal device, it may be considered that the network device requeststhe terminal device to feed back a precoding vector based on the secondfeedback mode. In this case, the foregoing fifth indication informationused to indicate the length of the frequency domain vector may beunderstood as an example of the sixth indication information.

It should be noted that a length of a space-frequency component vectormay be determined by both a length of a frequency domain vector and alength of a beam vector. Therefore, when the network device indicatesthe length of the frequency domain vector to the terminal device, theterminal device may feed back the PMI based on a port selection vectorand the frequency domain vector, or may feed back the PMI based on thespace-frequency vector. This is not limited in this application.

In step 320, the network device sends the sixth indication information.Correspondingly, the terminal device receives the sixth indicationinformation.

Optionally, the sixth indication information is carried in an RRCmessage.

A specific method for sending the sixth indication information by thenetwork device to the terminal device may be the same as a manner ofsending signaling by the network device to the terminal device in thecurrent technology. For brevity, detailed descriptions of a specificprocess of the sending method are omitted herein.

In step 330, the terminal device generates a PMI based on the feedbackmode indicated by the sixth indication information.

The terminal device may generate the PMI based on the feedback modeindicated by the sixth indication information. When the terminal devicegenerates the PMI based on the first feedback mode, a specific processin which the terminal device generates the PMI may be the same as thatin the current technology. For brevity, details are not describedherein. When the terminal device generates the PMI based on the secondfeedback mode, a specific implementation process has been described indetail in the foregoing method 200. For brevity, details are notdescribed herein again.

In step 340, the terminal device sends the PMI. Correspondingly, thenetwork device receives the PMI.

The terminal device may send the PMI to the network device, so that thenetwork device determines a precoding matrix. The network device may bethe foregoing network device that sends the sixth indicationinformation, or may be another network device. This is not limited inthis application. It should be understood that the step of sending thePMI by the terminal device to the network device shown in the figure ismerely an example, and should not constitute any limitation on thisapplication.

Then, the network device may determine the precoding matrix based on thePMI, to determine a precoding matrix used for data transmission. Thenetwork device may determine the precoding matrix based on the PMI byusing different feedback modes. When the terminal device generates thePMI based on the first feedback mode, a specific process in which thenetwork device determines the precoding matrix based on the PMI may bethe same as that in the current technology. For brevity, details are notdescribed herein. When the terminal device generates the PMI based onthe second feedback mode, a specific process in which the network devicedetermines the precoding matrix based on the PMI has been described indetail in the foregoing method 200. For brevity, details are notdescribed herein again.

Based on the foregoing method, the terminal device may feed back,according to an indication of the network device, the PMI by using acorresponding feedback mode. Different measurement cases may be used byintroducing a plurality of feedback modes, and both feedback precisionand feedback overheads may be considered, thereby achieving a balancebetween them.

It should be understood that sequence numbers of the processes do notmean execution sequences in the foregoing embodiments. The executionsequences of the processes should be determined according to functionsand internal logic of the processes, and should not be construed as anylimitation on the implementation processes of the embodiments of thisapplication.

With reference to FIG. 2 and FIG. 3 , the foregoing describes in detailthe methods for indicating and determining a precoding vector providedin the embodiments of this application. The following describes indetail a communications apparatus in the embodiments of this applicationwith reference to FIG. 4 to FIG. 6 .

FIG. 4 is a schematic block diagram of a communications apparatusaccording to an embodiment of this application. As shown in the figure,the communications apparatus 1000 may include a communications unit 1100and a processing unit 1200.

In a possible design, the communications apparatus 1000 may correspondto the terminal device in the foregoing method embodiments, for example,may be a terminal device, or may be a chip disposed in a terminaldevice.

Specifically, the communications apparatus 1000 may correspond to theterminal device in the method 200 or the method 300 in the embodimentsof this application. The communications apparatus 1000 may include unitsconfigured to perform the method 200 in FIG. 2 or the method 300 in FIG.3 performed by the terminal device. In addition, the units in thecommunications apparatus 1000 and the foregoing other operations and/orfunctions are separately intended to implement corresponding proceduresof the method 200 in FIG. 2 or the method 300 in FIG. 3 .

When the communications apparatus 1000 is configured to perform themethod 200 in FIG. 2 , the communications unit 1100 may be configured toperform step 220 in the method 200, and the processing unit 1200 may beconfigured to perform step 210 in the method 200.

Specifically, the processing unit 1200 may be configured to generatefirst indication information, where the first indication information isused to indicate L₁ beam vectors in a beam vector set, K₁ frequencydomain vectors in a frequency domain vector set, and T₁ space-frequencycomponent matrices, and a weighted sum of the T₁ space-frequencycomponent matrices is used to determine a precoding vector of one ormore frequency domain units. The L₁ beam vectors and the K₁ frequencydomain vectors correspond to M₁ space-frequency component matrices, theT₁ space-frequency component matrices are a part of the M₁space-frequency component matrices, each of the M₁ space-frequencycomponent matrices is uniquely determined by one of the L₁ beam vectorsand one of the K₁ frequency domain vectors, and M₁=L₁×K₁. The L₁ beamvectors are a part of beam vectors in the beam vector set, and/or the K₁frequency domain vectors are a part of frequency domain vectors in thefrequency domain vector set. M₁, L₁, K₁, and T₁ are all positiveintegers. The communications unit 1100 may be configured to send thefirst indication information.

Optionally, the communications unit 1100 is further configured toreceive second indication information, where the second indicationinformation is used to indicate a value or values of one or more of M₁,L₁, and K₁.

Optionally, the communications unit 1100 is further configured toreceive third indication information, where the third indicationinformation is used to indicate a value of T₁.

Optionally, the M₁ space-frequency component matrices are selected froma space-frequency component matrix set or a subset of a space-frequencycomponent matrix set, the space-frequency component matrices aredetermined by beam vectors in the beam vector set and frequency domainvectors in the frequency domain vector set, and each space-frequencycomponent matrix in the space-frequency component matrix set is uniquelydetermined by one beam vector in the beam vector set and one frequencydomain vector in the frequency domain vector set.

The first indication information includes location information of the M₁space-frequency component matrices in the space-frequency componentmatrix set or location information of the M₁ space-frequency componentmatrices in the subset of the space-frequency component matrix set.

Optionally, each of the M₁ space-frequency component matrices isdetermined by a product of one of the L₁ beam vectors and a conjugatetranspose of one of the K₁ frequency domain vectors.

Optionally, each of the M₁ space-frequency component matrices isdetermined by a Kronecker product of one of the K₁ frequency domainvectors and one of the L₁ beam vectors.

Optionally, the weighted sum of the T₁ space-frequency componentmatrices is used to determine a precoding vector of one or morefrequency domain units at a first transport layer.

Optionally, the processing unit 1200 is further configured to generatefourth indication information, where the fourth indication informationis used to indicate L₂ beam vectors in the beam vector set, K₂ frequencydomain vectors in the frequency domain vector set, and T₂space-frequency component matrices, and a weighted sum of the T₂space-frequency component matrices is used to determine a precodingvector of one or more frequency domain units at a second transportlayer. The L₂ beam vectors and the K₂ frequency domain vectorscorrespond to M₂ space-frequency component matrices, the T₂space-frequency component matrices are a part of the M₂ space-frequencycomponent matrices, each of the M₂ space-frequency component matrices isuniquely determined by one of the L₂ beam vectors and one of the K₂frequency domain vectors, and M₂=L₂×K₂; the L₂ beam vectors are a partof beam vectors in the beam vector set, and/or the K₂ frequency domainvectors are a part of frequency domain vectors in the frequency domainvector set; and M₂, L₂, K₂, and T₂ are all positive integers. Thecommunications unit 1100 is further configured to send the fourthindication information.

Optionally, L₁=L₂, K₁=K₂, and T₁=T₂.

Optionally, L₁>L₂, K₁>K₂, or T₁>T₂.

When the communications apparatus 1000 is configured to perform themethod 300 in FIG. 3 , the communications unit 1100 may be configured toperform step 320 and step 340 in the method 300, and the processing unit1200 may be configured to perform step 330 in the method 300.

It should be understood that a specific process in which each unitperforms the foregoing corresponding steps is described in detail in theforegoing method embodiment, and for brevity, details are not describedherein.

It should be further understood that, when the communications apparatus1000 is a terminal device, the communications unit 1100 in thecommunications apparatus 1000 may correspond to a transceiver 2020 in aterminal device 2000 shown in FIG. 5 , and the processing unit 1200 inthe communications apparatus 1000 may correspond to a processor 2010 inthe terminal device 2000 shown in FIG. 5 .

It should be further understood that when the communications apparatus1000 is a chip disposed in a terminal device, the communications unit1100 in the communications apparatus 1000 may be an input/outputinterface.

In another possible design, the communications apparatus 1000 maycorrespond to the network device in the foregoing method embodiments,for example, may be a network device, or may be a chip disposed in anetwork device.

Specifically, the communications apparatus 1000 may correspond to thenetwork device in the method 200 or the method 300 in the embodiments ofthis application. The communications apparatus 1000 may include unitsconfigured to perform the method 200 in FIG. 2 or the method 300 in FIG.3 performed by the network device. In addition, the units in thecommunications apparatus 1000 and the foregoing other operations and/orfunctions are separately intended to implement corresponding proceduresof the method 200 in FIG. 2 or the method 300 in FIG. 3 .

When the communications apparatus 1000 is configured to perform themethod 300 in FIG. 3 , the communications unit 1100 may be configured toperform step 220 in the method 200, and the processing unit 1200 may beconfigured to perform step 230 in the method 200.

Specifically, the communications unit 1100 may be configured to receivefirst indication information, where the first indication information isused to indicate L₁ beam vectors in a beam vector set, K₁ frequencydomain vectors in a frequency domain vector set, and T₁ space-frequencycomponent matrices, and a weighted sum of the T₁ space-frequencycomponent matrices is used to determine a precoding vector of one ormore frequency domain units. The L₁ beam vectors and the K₁ frequencydomain vectors correspond to M₁ space-frequency component matrices, theT₁ space-frequency component matrices are a part of the M₁space-frequency component matrices, each of the M₁ space-frequencycomponent matrices is uniquely determined by one of the L₁ beam vectorsand one of the K₁ frequency domain vectors, and M₁=L₁×K₁. The L₁ beamvectors are a part of beam vectors in the beam vector set, and/or the K₁frequency domain vectors are a part of frequency domain vectors in thefrequency domain vector set. M₁, L₁, K₁, and T₁ are all positiveintegers.

The processing unit 1200 may be configured to determine a precodingvector of one or more frequency domain units based on the firstindication information.

Optionally, the communications unit 1100 is further configured to sendsecond indication information, where the second indication informationis used to indicate a value or values of one or more of M₁, L₁, and K₁.

Optionally, the communications unit 1100 is further configured to sendthird indication information, where the third indication information isused to indicate a value of T₁.

Optionally, the M₁ space-frequency component matrices are selected froma space-frequency component matrix set or a subset of a space-frequencycomponent matrix set, the space-frequency component matrices aredetermined by beam vectors in the beam vector set and frequency domainvectors in the frequency domain vector set, and each space-frequencycomponent matrix in the space-frequency component matrix set is uniquelydetermined by one beam vector in the beam vector set and one frequencydomain vector in the frequency domain vector set.

The first indication information includes location information of the M₁space-frequency component matrices in the space-frequency componentmatrix set or location information of the M₁ space-frequency componentmatrices in the subset of the space-frequency component matrix set.

Optionally, each of the M₁ space-frequency component matrices isdetermined by a product of one of the L₁ beam vectors and a conjugatetranspose of one of the K₁ frequency domain vectors.

Optionally, each of the M₁ space-frequency component matrices isdetermined by a Kronecker product of one of the K₁ frequency domainvectors and one of the L₁ beam vectors.

Optionally, the weighted sum of the T₁ space-frequency componentmatrices is used to determine a precoding vector of one or morefrequency domain units at a first transport layer.

Optionally, the communications unit 1100 is further configured toreceive fourth indication information, where the fourth indicationinformation is used to indicate L₂ beam vectors in the beam vector set,K₂ frequency domain vectors in the frequency domain vector set, and T₂space-frequency component matrices, and a weighted sum of the T₂space-frequency component matrices is used to determine a precodingvector of one or more frequency domain units at a second transportlayer. The L₂ beam vectors and the K₂ frequency domain vectorscorrespond to M₂ space-frequency component matrices, the T₂space-frequency component matrices are a part of the M₂ space-frequencycomponent matrices, each of the M₂ space-frequency component matrices isuniquely determined by one of the L₂ beam vectors and one of the K₂frequency domain vectors, and M₂=L₂×K₂; the L₂ beam vectors are a partof beam vectors in the beam vector set, and/or the K₂ frequency domainvectors are a part of frequency domain vectors in the frequency domainvector set; and M₂, L₂, K₂, and T₂ are all positive integers. Theprocessing unit 1200 is further configured to determine a precodingvector of one or more frequency domain units at a second transport layerbased on the fourth indication information.

Optionally, L₁=L₂, K₁=K₂, and T₁=T₂.

Optionally, L₁>L₂, K₁>K₂, or T₁>T₂.

When the communications apparatus 1000 is configured to perform themethod 300 in FIG. 3 , the communications unit 1100 may be configured toperform step 320 and step 340 in the method 300, and the processing unit1200 may be configured to perform step 310 in the method 300.

It should be further understood that, when the communications apparatus1000 is a network device, the communications unit in the communicationsapparatus 1000 may correspond to a transceiver 3200 in a network device3000 shown in FIG. 6 , and the processing unit 1200 in thecommunications apparatus 1000 may correspond to a processor 3100 in thenetwork device 3000 shown in FIG. 6 .

It should be further understood that when the communications apparatus1000 is a chip disposed in a network device, the communications unit1100 in the communications apparatus 1000 may be an input/outputinterface.

FIG. 5 is a schematic structural diagram of the terminal device 2000according to an embodiment of this application. The terminal device 2000may be applied to the system shown in FIG. 1 , and perform a function ofthe terminal device in the foregoing method embodiments. As shown in thefigure, the terminal device 2000 includes the processor 2010 and thetransceiver 2020. Optionally, the terminal device 2000 further includesa memory 2030. The processor 2010, the transceiver 2020, and the memory2030 may communicate with each other by using an internal connectionpath, to transfer a control signal and/or a data signal. The memory 2030is configured to store a computer program. The processor 2010 isconfigured to invoke the computer program from the memory 2030 and runthe computer program, to control the transceiver 2020 to send andreceive a signal. Optionally, the terminal device 2000 may furtherinclude an antenna 2040, configured to send, by using a radio signal,uplink data or uplink control signaling output by the transceiver 2020.

The processor 2010 and the memory 2030 may be integrated into oneprocessing apparatus. The processor 2010 is configured to executeprogram code stored in the memory 2030 to implement the foregoingfunctions. During specific implementation, the memory 2030 may also beintegrated into the processor 2010, or may be independent of theprocessor 2010. The processor 2010 may correspond to the processing unitin FIG. 4 .

The transceiver 2020 may correspond to the communications unit in FIG. 4, and may also be referred to as a transceiver unit. The transceiver2020 may include a receiver (or referred to as a receiver or a receivercircuit) and a transmitter (or referred to as a transmitter or atransmitter circuit). The receiver is configured to receive a signal,and the transmitter is configured to transmit a signal.

It should be understood that, the terminal device 2000 shown in FIG. 5can implement each process performed by the terminal device in themethod embodiment in FIG. 2 . The operations and/or the functions of themodules in the terminal device 2000 are intended to implementcorresponding procedures in the foregoing method embodiment. Fordetails, refer to the descriptions in the foregoing method embodiment.To avoid repetition, detailed descriptions are properly omitted herein.

The processor 2010 may be configured to perform an action that isimplemented inside the terminal device and that is described in theforegoing method embodiment. The transceiver 2020 may be configured toperform an action that is of sending information by the terminal deviceto the network device or receiving information by the terminal devicefrom the network device and that is described in the foregoing methodembodiment. For details, refer to the descriptions in the foregoingmethod embodiment. Details are not described herein again.

Optionally, the terminal device 2000 may further include a power supply2050, configured to supply power to various components or circuits inthe terminal device.

In addition, to make functions of the terminal device more perfect, theterminal device 2000 may further include one or more of an input unit2060, a display unit 2070, an audio circuit 2080, a camera 2090, asensor 2100, and the like, and the audio circuit may further include aspeaker 2082, a microphone 2084, and the like.

FIG. 6 is a schematic structural diagram of a network device accordingto an embodiment of this application, for example, may be a schematicstructural diagram of a base station. The base station 3000 may beapplied to the system shown in FIG. 1 , and perform a function of thenetwork device in the foregoing method embodiment. As shown in thefigure, the base station 3000 may include one or more remote radio units(remote radio unit, RRU) 3100, and one or more baseband units (BBU)(which may also be referred to as distributed units (DU)) 3200. The RRU3100 may be referred to as a transceiver unit, and corresponds to thecommunications unit 1200 in FIG. 4 . Optionally, the transceiver unit3100 may also be referred to as a transceiver machine, a transceivercircuit, a transceiver, or the like, and may include at least oneantenna 3101 and a radio frequency unit 3102. Optionally, thetransceiver unit 3100 may include a receiving unit and a transmissionunit. The receiving unit may correspond to a receiver (or referred to asa receiver or a receiver circuit), and the transmission unit maycorrespond to a transmitter (or referred to as a transmitter or atransmitter circuit). The RRU 3100 is mainly configured to receive andsend a radio frequency signal and perform conversion between a radiofrequency signal and a baseband signal, for example, configured to sendindication information to a terminal device. The BBU 3200 is mainlyconfigured to: perform baseband processing, control the base station,and so on. The RRU 3100 and the BBU 3200 may be physically disposedtogether, or may be physically disposed separately, where to bespecific, the base station is a distributed base station.

The BBU 3200 is a control center of the base station, or may be referredto as a processing unit. The BBU may correspond to the processing unit1100 in FIG. 4 , and is mainly configured to implement a basebandprocessing function, for example, channel coding, multiplexing,modulation, or spreading. For example, the BBU (the processing unit) maybe configured to control the base station to perform an operationprocedure related to the network device in the foregoing methodembodiment, for example, generate the foregoing indication information.

In an example, the BBU 3200 may include one or more boards, and aplurality of boards may jointly support a radio access network (forexample, an LTE network) having a single access standard, or mayseparately support radio access networks (for example, an LTE network, a5G network, or another network) having different access standards. TheBBU 3200 further includes a memory 3201 and a processor 3202. The memory3201 is configured to store a necessary instruction and necessary data.The processor 3202 is configured to control the base station to performa necessary action, for example, configured to control the base stationto perform the operation procedure related to the network device in theforegoing method embodiment. The memory 3201 and the processor 3202 mayserve one or more boards. In other words, the memory and the processormay be independently disposed on each board. Alternatively, theplurality of boards may share a same memory and a same processor. Inaddition, each board may further be provided with a necessary circuit.

It should be understood that the base station 3000 shown in FIG. 6 canimplement processes related to the network device in the methodembodiment in FIG. 2 . The operations and/or the functions of themodules in the base station 3000 are intended to implement correspondingprocedures in the foregoing method embodiment. For details, refer to thedescriptions in the foregoing method embodiment. To avoid repetition,detailed descriptions are properly omitted herein.

The BBU 3200 may be configured to perform an action that is implementedinside the network device and that is described in the foregoing methodembodiment. The RRU 3100 may be configured to perform an action that isof sending information by the network device to the terminal device orreceiving information by the network device from the terminal device andthat is described in the foregoing method embodiment. For details, referto the descriptions in the foregoing method embodiment. Details are notdescribed herein again.

An embodiment of this application further provides a processingapparatus, including a processor and an interface. The processor isconfigured to perform the method in any foregoing method embodiment.

It should be understood that the processing apparatus may be one or morechips. For example, the processing apparatus may be a field programmablegate array (field programmable gate array, FPGA), anapplication-specific integrated chip (application specific integratedcircuit, ASIC), a system on chip (system on chip, SoC), a centralprocessing unit (central processor unit, CPU), a network processor(network processor, NP), a digital signal processing circuit (digitalsignal processor, DSP), a microcontroller unit (micro controller unit,MCU), a programmable controller (programmable logic device, PLD), oranother integrated chip.

In an implementation process, steps in the foregoing methods can beimplemented by using a hardware integrated logic circuit in theprocessor, or by using instructions in a form of software. The steps ofthe methods disclosed with reference to the embodiments of thisapplication may be directly performed by a hardware processor, or may beperformed by a combination of hardware and software modules in theprocessor. The software module may be located in a mature storage mediumin the field, such as a random access memory, a flash memory, aread-only memory, a programmable read-only memory, an electricallyerasable programmable memory, or a register. The storage medium islocated in the memory, and the processor reads information in the memoryand completes the steps in the foregoing methods in combination with thehardware of the processor. To avoid repetition, details are notdescribed herein again.

It should be noted that, the processor in the embodiments of thisapplication may be an integrated circuit chip, and has a signalprocessing capability. In an implementation process, the steps in theforegoing method embodiments may be completed through a hardwareintegrated logical circuit in the processor or an instruction in a formof software. The processor may be a general-purpose processor, a digitalsignal processor (DSP), an application-specific integrated circuit(ASIC), a field programmable gate array (FPGA) or another programmablelogic device, a discrete gate or a transistor logic device, or adiscrete hardware component. The methods, steps, and logical blockdiagrams that are disclosed in the embodiments of this application maybe implemented or performed. The general-purpose processor may be amicroprocessor, or the processor may be any conventional processor orthe like. The steps of the method disclosed with reference to theembodiments of this application may be directly executed and completedby a hardware decoding processor, or may be executed and completed by acombination of hardware and software modules in the decoding processor.The software module may be located in a mature storage medium in thefield, such as a random access memory, a flash memory, a read-onlymemory, a programmable read-only memory, an electrically erasableprogrammable memory, or a register. The storage medium is located in thememory, and the processor reads information in the memory and completesthe steps in the foregoing methods in combination with the hardware ofthe processor.

It may be understood that the memory in the embodiments of thisapplication may be a volatile memory or a nonvolatile memory, or mayinclude both a volatile memory and a nonvolatile memory. The nonvolatilememory may be a read-only memory (read-only memory, ROM), a programmableread-only memory (programmable ROM, PROM), an erasable programmableread-only memory (erasable PROM, EPROM), an electrically erasableprogrammable read-only memory (electrically EPROM, EEPROM), or a flashmemory. The volatile memory may be a random access memory (random accessmemory, RAM), and is used as an external cache. Through exampledescription but not limitative description, many forms of RAMs may beused, for example, a static random access memory (static RAM, SRAM), adynamic random access memory (dynamic RAM, DRAM), a synchronous dynamicrandom access memory (synchronous DRAM, SDRAM), a double data ratesynchronous dynamic random access memory (double data rate SDRAM, DDRSDRAM), an enhanced synchronous dynamic random access memory (enhancedSDRAM, ESDRAM), a synchlink dynamic random access memory (synchlinkDRAM, SLDRAM), and a direct rambus random access memory (direct rambusRAM, DR RAM). It should be noted that the memory of the systems andmethods described in this specification includes but is not limited tothese and any memory of another proper type.

Based on the method provided in the embodiments of this application,this application further provides a computer program product. Thecomputer program product includes computer program code. When thecomputer program code is run on a computer, the computer is enabled toperform the method in any one of the embodiments shown in FIG. 2 .

According to the method provided in the embodiments of this application,this application further provides a computer-readable medium. Thecomputer-readable medium stores program code. When the program code isrun on a computer, the computer is enabled to perform the method in anyone of the embodiments shown in FIG. 2 .

According to the method provided in the embodiments of this application,this application further provides a system. The system includes theforegoing one or more terminal devices and one or more network devices.

All or some of the foregoing embodiments may be implemented throughsoftware, hardware, firmware, or any combination thereof. When softwareis used to implement the embodiments, all or some of the embodiments maybe implemented in a form of a computer program product. The computerprogram product includes one or more computer instructions. When thecomputer instructions are loaded and executed on a computer, theprocedures or functions according to the embodiments of this applicationare all or partially generated. The computer may be a general-purposecomputer, a special-purpose computer, a computer network, or otherprogrammable apparatuses. The computer instructions may be stored in acomputer-readable storage medium or may be transmitted from acomputer-readable storage medium to another computer-readable storagemedium. For example, the computer instructions may be transmitted from awebsite, computer, server, or data center to another website, computer,server, or data center in a wired (for example, a coaxial cable, anoptical fiber, or a digital subscriber line (digital subscriber line,DSL)) or wireless (for example, infrared, radio, or microwave) manner.The computer-readable storage medium may be any usable medium accessibleby the computer, or a data storage device, such as a server or a datacenter, integrating one or more usable media. The usable medium may be amagnetic medium (for example, a floppy disk, a hard disk, or a magnetictape), an optical medium (for example, a high-density digital video disc(digital video disc, DVD)), a semiconductor medium (for example, asolid-state drive (solid state disc, SSD)), or the like.

The network device and the terminal device in the foregoing apparatusembodiments are corresponding to the network device or the terminaldevice in the method embodiments, and a corresponding module or unitperforms a corresponding step. For example, a communications unit (atransceiver) performs a receiving step or a sending step in the methodembodiments, and a processing unit (a processor) may perform steps otherthan the sending or receiving step. For a function of a specific unit,refer to a corresponding method embodiment. There may be one or moreprocessors.

The terms such as “component”, “module”, and “system” used in thisspecification are used to indicate computer-related entities, hardware,firmware, combinations of hardware and software, software, or softwarebeing executed. For example, a component may be, but is not limited to,a process that runs on a processor, a processor, an object, anexecutable file, an execution thread, a program, and/or a computer. Asshown in figures, both a computing device and an application running ona computing device may be components. One or more components may residewithin a process and/or an execution thread, and a component may belocated on one computer and/or distributed between two or morecomputers. In addition, these components may be executed from variouscomputer readable media that store various data structures. For example,the components may communicate by using a local and/or remote processand according to, for example, a signal having one or more data packets(for example, data from two components interacting with anothercomponent in a local system, a distributed system, and/or across anetwork such as the internet interacting with another system by usingthe signal).

A person of ordinary skill in the art may be aware that, in combinationwith various illustrative logical blocks (illustrative logical block)and steps (step) described in the embodiments disclosed in thisspecification may be implemented by electronic hardware or a combinationof computer software and electronic hardware. Whether the functions areperformed by hardware or software depends on a particular applicationand a design constraint of the technical solutions. A person skilled inthe art may use different methods to implement the described functionsfor each particular application, but it should not be considered thatsuch an implementation goes beyond the scope of this application.

It may be clearly understood by a person skilled in the art that for thepurpose of convenient and brief description, for a detailed workingprocess of the described system, apparatus, and unit, refer to acorresponding process in the foregoing method embodiments.

In the embodiments provided in this application, it should be understoodthat the disclosed system, apparatus, and methods may be implemented inanother manner. For example, the described apparatus embodiments aremerely examples. For example, the division of units is merely logicalfunction division and may be other division during actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented by using some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electrical, mechanical, or another form.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected based on actualrequirements to achieve the objectives of the solutions of theembodiments.

In addition, functional units in the embodiments of this application maybe integrated into one processing unit, or each of the units may existalone physically, or two or more units are integrated into one unit.

In the foregoing embodiments, all or some of the functions of thefunctional units may be implemented by software, hardware, firmware, orany combination thereof. When software is used to implement theembodiments, all or some of the embodiments may be implemented in a formof a computer program product. The computer program product includes oneor more computer instructions (programs). When the computer programinstructions (programs) are loaded and executed on a computer, theprocedure or functions according to the embodiments of this applicationare all or partially generated. The computer may be a general-purposecomputer, a special-purpose computer, a computer network, or otherprogrammable apparatuses. The computer instructions may be stored in acomputer-readable storage medium or may be transmitted from acomputer-readable storage medium to another computer-readable storagemedium. For example, the computer instructions may be transmitted from awebsite, computer, server, or data center to another website, computer,server, or data center in a wired (for example, a coaxial cable, anoptical fiber, or a digital subscriber line (DSL)) or wireless (forexample, infrared, radio, and microwave, or the like) manner. Thecomputer-readable storage medium may be any usable medium accessible bythe computer, or a data storage device, such as a server or a datacenter, integrating one or more usable media. The usable medium may be amagnetic medium (for example, a floppy disk, a hard disk, or a magnetictape), an optical medium (for example, a DVD), a semiconductor medium(for example, a solid-state drive (solid state disk, SSD)), or the like.

When the functions are implemented in a form of a software functionalunit and sold or used as an independent product, the functions may bestored in a computer-readable storage medium. Based on such anunderstanding, the technical solutions of this application essentially,or the part contributing to the current technology, or some of thetechnical solutions may be implemented in a form of a software product.The software product is stored in a storage medium, and includes severalinstructions for instructing a computer device (which may be a personalcomputer, a server, or a network device) to perform all or some of thesteps of the method described in the embodiments of this application.The storage medium includes any medium that can store program code, suchas a USB flash drive, a removable hard disk, a read-only memory(read-only memory, ROM), a random access memory (random access memory,RAM), a magnetic disk, or an optical disc.

The foregoing descriptions are merely specific implementations of thisapplication, but are not intended to limit the protection scope of thisapplication. Any variation or replacement readily figured out by aperson skilled in the art within the technical scope disclosed in thisapplication shall fall within the protection scope of this application.Therefore, the protection scope of this application shall be subject tothe protection scope of the claims.

1. A method comprising: generating, by a terminal apparatus, firstindication information, wherein the first indication informationindicates L₁ space domain vectors in a space domain vector set, K₁frequency domain vectors in a frequency domain vector set, and T₁space-frequency component matrices, wherein a precoding vector of one ormore frequency domain units is determined by a weighted sum of the T₁space-frequency component matrices, wherein the L₁ space domain vectorsand the K₁ frequency domain vectors correspond to M₁ space-frequencycomponent matrices that comprise the T₁ space-frequency componentmatrices, wherein each of the M₁ space-frequency component matrices isuniquely determined by a different combination of one of the L₁ spacedomain vectors and one of the K₁ frequency domain vectors, and whereinM₁=L₁×K₁, M₁, L₁, K₁, and T₁ are positive integers, and T₁ is less thanM₁; and sending, by the terminal apparatus, the first indicationinformation to a network apparatus.
 2. The method according to claim 1,wherein the method further comprises: receiving, by the terminalapparatus, second indication information, wherein the second indicationinformation indicates one or more of M₁, L₁, and K₁.
 3. The methodaccording to claim 1, wherein K₁ is smaller when a quantity of transportlayers is greater than a preset threshold.
 4. The method according toclaim 1, wherein the first indication information comprises locationinformation of the L₁ space domain vectors in the space domain vectorset and location information of the K₁ frequency domain vectors in thefrequency domain vector set.
 5. The method according to claim 1, whereinthe M₁ space-frequency component matrices are selected from aspace-frequency component matrix set, wherein each space-frequencycomponent matrix in the space-frequency component matrix set is uniquelydetermined by a different combination of one space domain vector in thespace domain vector set and one frequency domain vector in the frequencydomain vector set, and wherein the first indication informationcomprises location information of the M₁ space-frequency componentmatrices in the space-frequency component matrix set.
 6. The methodaccording to claim 1, wherein each of the M₁ space-frequency componentmatrices is determined by a product of one of the L₁ space domainvectors and a conjugate transpose of one of the K₁ frequency domainvectors.
 7. The method according to claim 1, wherein the precodingvector is determined for a transport layer.
 8. The method according toclaim 1, wherein a length of the frequency domain vector is a quantityof frequency domain units to be reported included in a frequency domainoccupation bandwidth of a channel state information (CSI) measurementresource configured for the terminal apparatus.
 9. The method accordingto claim 1, wherein the M₁ space-frequency component matrices correspondto M₁ bits, and wherein the T₁ space-frequency component matrices areindicated by bits in the M₁ bits with values of
 1. 10. The methodaccording to claim 9, wherein the M₁ bits corresponding to the M₁space-frequency component matrices are sorted based on an order ofsequentially traversing the L₁ space domain vectors and the K₁ frequencydomain vectors according to: (v_(s) ⁰, v_(f) ⁰) (v_(s) ¹, v_(f) ⁰), . .. , (v_(s) ^(L) ¹ ⁻¹, v_(f) ⁰), (v_(s) ⁰, v_(f) ¹), (v_(s) ¹, v_(f) ¹),. . . , (v_(s) ^(L) ¹ ⁻¹, v_(f) ^(K) ¹ ⁻¹), where v_(s) ⁰, v_(s) ¹, . .. , v_(s) ^(L) ¹ ⁻¹ represent the L₁ spatial domain vectors, v_(f) ⁰,v_(f) ¹, . . . , v_(f) ^(K) ¹ ⁻¹ represent the K₁ frequency domainvectors.
 11. The method according to claim 1, wherein the firstindication information further indicates quantization information ofweighting coefficients of the T₁ space-frequency component matrices. 12.The method according to claim 11, wherein the weighting coefficients ofthe T₁ space-frequency component matrices are indicated based on anormalization process.
 13. The method according to claim 12, wherein thenormalization process comprises: indicating a weighting coefficient witha maximum modulus by indicating a location of the weighting coefficientin T₁ weighting coefficients in a matrix W′; and indicating quantizationinformation of remaining T₁−1 weight coefficients of the T₁ weightingcoefficients based on an index of a quantized relative value of each ofthe remaining T₁−1 weighting coefficients relative to the weightingcoefficient with the maximum modulus, wherein a dimension of the matrixW′ is L₁×K₁.
 14. The method of claim 13, wherein the weightingcoefficient with the maximum modulus is determined based on apolarization direction or a transport layer.
 15. A method comprising:receiving, by a network apparatus from a terminal apparatus, firstindication information, wherein the first indication informationindicates L₁ space domain vectors in a space domain vector set, K₁frequency domain vectors in a frequency domain vector set, and T₁space-frequency component matrices, wherein a precoding vector of one ormore frequency domain units is determined by a weighted sum of the T₁space-frequency component matrices, wherein the L₁ space domain vectorsand the K₁ frequency domain vectors correspond to M₁ space-frequencycomponent matrices that comprise the T₁ space-frequency componentmatrices, wherein each of the M₁ space-frequency component matrices isuniquely determined by a different combination of one of the L₁ spacedomain vectors and one of the K₁ frequency domain vectors, and whereinM₁=L₁×K₁, M₁, L₁, K₁, and T₁ are positive integers, and T₁ is less thanM₁; and determining, by the network apparatus, the precoding vector ofthe one or more frequency domain units based on the first indicationinformation.
 16. The method according to claim 15, wherein the methodfurther comprises: sending, by the network apparatus, second indicationinformation, wherein the second indication information indicates one ormore values of one or more of M₁, L₁, and K₁.
 17. The method accordingto claim 15, wherein K₁ has-a is smaller when a quantity of transportlayers is greater than a preset threshold.
 18. The method according toclaim 15, wherein the first indication information comprises locationinformation of the L₁ space domain vectors in the space domain vectorset and location information of the K₁ frequency domain vectors in thefrequency domain vector set.
 19. The method according to claim 15,wherein the M₁ space-frequency component matrices are selected from aspace-frequency component matrix set, wherein each space-frequencycomponent matrix in the space-frequency component matrix set is uniquelydetermined by a different combination of one space domain vector in thespace domain vector set and one frequency domain vector in the frequencydomain vector set, and wherein the first indication informationcomprises location information of the M₁ space-frequency componentmatrices in the space-frequency component matrix set.
 20. The methodaccording to claim 15, wherein each of the M₁ space-frequency componentmatrices is determined by a product of one of the L₁ space domainvectors and a conjugate transpose of one of the K₁ frequency domainvectors.
 21. The method according to claim 15, wherein the precodingvector is determined for a transport layer.
 22. The method according toclaim 15, wherein a length of the frequency domain vector is a quantityof frequency domain units to be reported included in a frequency domainoccupation bandwidth of a channel state information (CSI) measurementresource configured for the terminal apparatus.
 23. The method accordingto claim 15, wherein the M₁ space-frequency component matricescorrespond to M₁ bits, and wherein the T₁ space-frequency componentmatrices are indicated by bits in the M₁ bits with values of
 1. 24. Themethod according to claim 23, wherein the M₁ bits corresponding to theM₁ space-frequency component matrices are sorted based on an order ofsequentially traversing the L₁ space domain vectors and the K₁ frequencydomain vectors according to: (v_(s) ⁰, v_(f) ⁰) (v_(s) ¹, v_(f) ⁰), . .. , (v_(s) ^(L) ¹ ⁻¹, v_(f) ⁰), (v_(s) ⁰, v_(f) ¹), (v_(s) ¹, v_(f) ¹),. . . , (v_(s) ^(L) ¹ ⁻¹, v_(f) ^(K) ¹ ⁻¹), where v_(s) ⁰, v_(s) ¹, . .. , v_(s) ^(L) ¹ ⁻¹ represent the L₁ spatial domain vectors, v_(f) ⁰,v_(f) ¹, . . . , v_(f) ^(K) ¹ ⁻¹ represent the K₁ frequency domainvectors.
 25. The method according to claim 15, wherein the firstindication information further indicates quantization information ofweighting coefficients of the T₁ space-frequency component matrices. 26.The method according to claim 25, wherein the weighting coefficients ofthe T₁ space-frequency component matrices are indicated based on anormalization process.
 27. The method according to claim 26, wherein thenormalization process comprises: indicating a weighting coefficient witha maximum modulus by indicating a location of the weighting coefficientin T₁ weighting coefficients in a matrix W′; and indicating quantizationinformation of remaining T₁−1 weight coefficients of the T₁ weightingcoefficients based on an index of a quantized relative value of each ofthe remaining T₁−1 weighting coefficients relative to the weightingcoefficient with the maximum modulus, wherein a dimension of the matrixW′ is L₁×K₁.
 28. The method of claim 27, wherein the weightingcoefficient with the maximum modulus is determined based on apolarization direction or a transport layer.
 29. A communicationsapparatus, comprising at least one processor, and one or more memoriescoupled to the at least one processor and storing programminginstructions for execution by the at least one processor to performoperations comprising: generating first indication information, whereinthe first indication information indicates L₁ space domain vectors in aspace domain vector set, K₁ frequency domain vectors in a frequencydomain vector set, and T₁ space-frequency component matrices, wherein aprecoding vector of one or more frequency domain units is determined bya weighted sum of the T₁ space-frequency component matrices, wherein theL₁ space domain vectors and the K₁ frequency domain vectors correspondto M₁ space-frequency component matrices that comprise the T₁space-frequency component matrices, wherein each of the M₁space-frequency component matrices is uniquely determined by a differentcombination of one of the L₁ space domain vectors and one of the K₁frequency domain vectors, and wherein M₁=L₁×K₁, M₁, L₁, K₁, and T₁ arepositive integers, and T₁ is less than M₁; and sending the firstindication information to a network apparatus.
 30. The apparatusaccording to claim 29, wherein the operations further comprisesreceiving second indication information, wherein the second indicationinformation indicates one or more of M₁, L₁, and K₁.
 31. The apparatusaccording to claim 29, wherein K₁ is smaller when a quantity oftransport layers is greater than a preset threshold.
 32. The apparatusaccording to claim 29, wherein the first indication informationcomprises location information of the L₁ space domain vectors in thespace domain vector set and location information of the K₁ frequencydomain vectors in the frequency domain vector set.
 33. The apparatusaccording to claim 29, wherein the M₁ space-frequency component matricesare selected from a space-frequency component matrix set, wherein eachspace-frequency component matrix in the space-frequency component matrixset is uniquely determined by a different combination of one spacedomain vector in the space domain vector set and one frequency domainvector in the frequency domain vector set, and wherein the firstindication information comprises location information of the M₁space-frequency component matrices in the space-frequency componentmatrix set.
 34. The apparatus according to claim 29, wherein each of theM₁ space-frequency component matrices is determined by a product of oneof the L₁ space domain vectors and a conjugate transpose of one of theK₁ frequency domain vectors.
 35. The apparatus according to claim 29,wherein the precoding vector is determined for a transport layer. 36.The apparatus according to claim 29, wherein a length of the frequencydomain vector is a quantity of frequency domain units to be reportedincluded in a frequency domain occupation bandwidth of a channel stateinformation (CSI) measurement resource configured for a terminalapparatus.
 37. The apparatus according to claim 29, wherein the M₁space-frequency component matrices correspond to M₁ bits, and whereinthe T₁ space-frequency component matrices are indicated by bits in theM₁ bits with values of
 1. 38. The apparatus according to claim 37,wherein the M₁ bits corresponding to the M₁ space-frequency componentmatrices are sorted based on an order of sequentially traversing the L₁space domain vectors and the K₁ frequency domain vectors according to:(v_(s) ⁰, v_(f) ⁰) (v_(s) ¹, v_(f) ⁰), . . . , (v_(s) ^(L) ¹ ⁻¹, v_(f)⁰), (v_(s) ⁰, v_(f) ¹), (v_(s) ¹, v_(f) ¹), . . . , (v_(s) ^(L) ¹ ⁻¹,v_(f) ^(K) ¹ ⁻¹), where v_(s) ⁰, v_(s) ¹, . . . , v_(s) ^(L) ¹ ⁻¹represent the L₁ spatial domain vectors, v_(f) ⁰, v_(f) ¹, . . . , v_(f)^(K) ¹ ⁻¹ represent the K₁ frequency domain vectors.
 39. The apparatusaccording to claim 29, wherein the first indication information furtherindicates quantization information of weighting coefficients of the T₁space-frequency component matrices.
 40. The apparatus according to claim39, wherein the weighting coefficients of the T₁ space-frequencycomponent matrices are indicated based on a normalization process. 41.The apparatus according to claim 40, wherein the normalization processcomprises: indicating a weighting coefficient with a maximum modulus byindicating a location of the weighting coefficient in T₁ weightingcoefficients in a matrix W′; and indicating quantization information ofremaining T₁−1 weight coefficients of the T₁ weighting coefficientsbased on an index of a quantized relative value of each of the remainingT₁−1 weighting coefficients relative to the weighting coefficient withthe maximum modulus, wherein a dimension of the matrix W′ is L₁×K₁. 42.The apparatus according to claim 41, wherein the weighting coefficientwith the maximum modulus is determined based on a polarization directionor a transport layer.
 43. The apparatus according to claim 29, whereinthe apparatus is a device or a chip.
 44. A communications apparatus,comprising at least one processor, and one or more memories coupled tothe at least one processor and storing programming instructions forexecution by the at least one processor to perform operationscomprising: receiving first indication information, wherein the firstindication information indicates L₁ space domain vectors in a spacedomain vector set, K₁ frequency domain vectors in a frequency domainvector set, and T₁ space-frequency component matrices, wherein aprecoding vector of one or more frequency domain units is determined bya weighted sum of the T₁ space-frequency component matrices, wherein theL₁ space domain vectors and the K₁ frequency domain vectors correspondto M₁ space-frequency component matrices that comprise the T₁space-frequency component matrices, wherein each of the M₁space-frequency component matrices is uniquely determined by a differentcombination of one of the L₁ space domain vectors and one of the K₁frequency domain vectors, and wherein M₁=L₁×K₁, M₁, L₁, K₁, and T₁ arepositive integers, and T₁ is less than M₁; and determining the precodingvector of the one or more frequency domain units based on the firstindication information.
 45. The apparatus according to claim 44, theoperations further comprising sending second indication information,wherein the second indication information indicates one or more of M₁,L₁, and K₁.
 46. The apparatus according to claim 44, wherein K₁ issmaller when a quantity of transport layers is greater than a presetthreshold.
 47. The apparatus according to claim 44, wherein the firstindication information comprises location information of the L₁ spacedomain vectors in the space domain vector set and location informationof the K₁ frequency domain vectors in the frequency domain vector set.48. The apparatus according to claim 44, wherein the M₁ space-frequencycomponent matrices are selected from a space-frequency component matrixset, wherein each space-frequency component matrix in thespace-frequency component matrix set is uniquely determined by adifferent combination of one space domain vector in the space domainvector set and one frequency domain vector in the frequency domainvector set, and wherein the first indication information compriseslocation information of the M₁ space-frequency component matrices in thespace-frequency component matrix set.
 49. The apparatus according toclaim 44, wherein each of the M₁ space-frequency component matrices isdetermined by a product of one of the L₁ space domain vectors and aconjugate transpose of one of the K₁ frequency domain vectors.
 50. Theapparatus according to claim 44, wherein the precoding vector determinedby the weighted sum of the T₁ space-frequency component matrices is fora transport layer.
 51. The apparatus according to claim 44, wherein alength of the frequency domain vector is a quantity of frequency domainunits to be reported included in a frequency domain occupation bandwidthof a channel state information (CSI) measurement resource configured forthe terminal apparatus.
 52. The apparatus according to claim 44, whereinthe M₁ space-frequency component matrices correspond to M₁ bits, andwherein the T₁ space-frequency component matrices are indicated by bitsin the M₁ bits with values of
 1. 53. The apparatus according to claim52, wherein the M₁ bits corresponding to the M₁ space-frequencycomponent matrices are sorted based on an order of sequentiallytraversing the L₁ space domain vectors and the K₁ frequency domainvectors according to: (v_(s) ⁰, v_(f) ⁰) (v_(s) ¹, v_(f) ⁰), . . . ,(v_(s) ^(L) ¹ ⁻¹, v_(f) ⁰), (v_(s) ⁰, v_(f) ¹), (v_(s) ¹, v_(f) ¹), . .. , (v_(s) ^(L) ¹ ⁻¹, v_(f) ^(K) ¹ ⁻¹), where v_(s) ⁰, v_(s) ¹, . . . ,v_(s) ^(L) ¹ ⁻¹ represent the L₁ spatial domain vectors, v_(f) ⁰, v_(f)¹, . . . , v_(f) ^(K) ¹ ⁻¹ represent the K₁ frequency domain vectors.54. The apparatus according to claim 44, wherein the first indicationinformation further indicates quantization information of weightingcoefficients of the T₁ space-frequency component matrices.
 55. Theapparatus according to claim 54, wherein the weighting coefficients ofthe T₁ space-frequency component matrices are indicated based on anormalization process.
 56. The apparatus according to claim 55, whereinthe normalization process comprises: indicating a weighting coefficientwith a maximum modulus by indicating a location of the weightingcoefficient in T₁ weighting coefficients in a matrix W′; and indicatingquantization information of remaining T₁−1 weight coefficients of the T₁weighting coefficients based on an index of a quantized relative valueof each of the remaining T₁−1 weighting coefficients relative to theweighting coefficient with the maximum modulus, wherein a dimension ofthe matrix W′ is L₁×K₁.
 57. The apparatus according to claim 56, whereinthe weighting coefficient with the maximum modulus is determined basedon a polarization direction or a transport layer.
 58. The apparatusaccording to claim 44, wherein the apparatus is a device or a chip.